[PERF-303] Integer XBlocks/XModules into the static asset pipeline.

This PR, based on hackathon work from Christina/Andy, implements a way to discover all installed XBlocks and XModules and to enumerate their public assets, then pulling them in during the collectstatic phase and hashing them.  In turn, the methods for generating URLs to resources will then returned the hashed name for assets, allowing them to be served from nginx/CDNs, and cached heavily.

* mattdrayer:  Latest proto code
* mattdrayer:  Add translation.py
* asadiqbal08: Xblock translation ugettext update, remove translation.py
* mattdrayer:  Additional I18N work -- starting to see some translations!
* asadiqbal08: Trying to make xBlock message catalog files path dynamic
* mattdrayer:  Remove unnecessary modifications
* mattdrayer:  Cleaned up implementation
* mattdrayer:  Moved import statement
* asadiqbal08: update as suggested
* asadiqbal08: xblock its own domain
* asadiqbal08: translation: secure none object
* asadiqbal08: pylint
* asadiqbal08: get locale from xblock
* asadiqbal08: update
* mattdrayer:  Determine XBlock locale path within runtime service
* mattdrayer:  Determine module location via the runtime
* mattdrayer:  Remove ModuleI18nService reference
* asadiqbal08: override the service in studio
* asadiqbal08: remove import
* asadiqbal08: update the Modulei18nService
* asadiqbal08: update the Modulei18nService
* mattdrayer:  Remove redundant __class__ reference
* asadiqbal08: update the docstring
* asadiqbal08: tests
* mattdrayer:  Remove specific ugettext override from ModuleI18nService
* mattdrayer:  Move service operation to base class
* mattdrayer:  Address quality violations
* asadiqbal08: Investigating the test failure issue on jenkins and solved
* asadiqbal08: First utilizing the parent class method
* mattdrayer:  Use recommended callable approach
* asadiqbal08: remove unused code
* asadiqbal08: Updated the test to use cms preview module system runtime in order to get i18n service.
* asadiqbal08: Pylint quality
* asadiqbal08: update the service call to check xblock declarations
* asadiqbal08: update doc string
* asadiqbal08: i18n callable test in studio
* asadiqbal08: test lms runtime for modulei18n service
* asadiqbal08: add doc strings
* asadiqbal08: Rename locale and domain to Flask-Babel convention

* The LMS now also monkey-patches
  xmodule.x_module.descriptor_global_handler_url and
  xmodule.x_module.descriptor_global_local_resource_url so that we can
  get LMS XBlock URLs from the DescriptorSystem. That functionality is
  needed in the block transforms collect() phase for certain XModules
  like Video. For instance, say we want to generate the transcripts
  URLs. The collect phase is run asynchronously, without a user context.

* The URL handler monkey-patching is now done in the startup.py files
  for LMS and Studio. Studio used to do this in the import of
  cms/djangoapps/contentstore/views/item.py. This was mostly just
  because it seemed like a sane and consistent place to put it.

* LmsHandlerUrls was removed, its handler_url and local_resource_url
  methods were moved to be top level functions. The only reason that
  class existed seems to be to give a place to store course_id state,
  and that can now be derived from the block location.

* To avoid the Module -> Descriptor ProxyAttribute magic that we do
  (which explodes with an UndefinedContext error because there is no
  user involved), when examining the block's handler method in
  handler_url, I made a few changes:

** Check the .__class__ to see if the handler was defined, instead of the
   block itself.

** The above required me to relax the check for _is_xblock_handler on the
   function, since that will no longer be defined.

90% of this goes away when we kill XModules and do the refactoring we've
wanted to do for a while.

TNL-1493

See https://openedx.atlassian.net/wiki/display/TNL/User+API for details

xblock-external-ui: Include CSRF token in the API answer
xblock-external-ui: Include full path when building local_url
xblock-external-ui: Fix TestHandleXBlockCallback & bok_choy, add tests
xblock-external-ui: Only return `instance` in `_invoke_xblock_handler()`
xblock-external-ui: Group resources by hash tag to avoid duplicate loads
xblock-external-ui: PEP8
xblock-external-ui: Fail early if the XBlock view is called anonymously

    We used to serve anonymous requests, but most XBlocks assume that the
    user is logged in, which can generate a lot of errors when the user is
    accessed or when an XBlock ajax callback is queried. Fail early to only
    get one error per page load, and prevent displaying the XBlock
    altogether when the LMS doesn't find an active user session.

xblock-external-ui: Add request params in view render context
xblock-external-ui: HTTP error status when file is too large for handler
xblock-external-ui: Fix unicode encodings in XBlock rendering
xblock-external-ui: Feature flag for API call ENABLE_XBLOCK_VIEW_ENDPOINT

TNL-498

PLAT-280

PLAT-221

[PLAT-217]

Move lms.lib.xblock into lms.djangoapps.lms_xblock in preparation add database backed configuration to it

TNL-649

[PLAT-191]

This commit adds the non-courseware lms/djangoapps and lms/lib.

These keys are now objects with a limited interface, and the particular
internal representation is managed by the data storage layer (the
modulestore).

For the LMS, there should be no outward-facing changes to the system.
The keys are, for now, a change to internal representation only. For
Studio, the new serialized form of the keys is used in urls, to allow
for further migration in the future.

Co-Author: Andy Armstrong <andya@edx.org>
Co-Author: Christina Roberts <christina@edx.org>
Co-Author: David Baumgold <db@edx.org>
Co-Author: Diana Huang <dkh@edx.org>
Co-Author: Don Mitchell <dmitchell@edx.org>
Co-Author: Julia Hansbrough <julia@edx.org>
Co-Author: Nimisha Asthagiri <nasthagiri@edx.org>
Co-Author: Sarina Canelake <sarina@edx.org>

[LMS-2370]

Also fixes STUD-1351

Adds a split_test_module XModule, that can choose one of its children
to display, based on a get_condition_for_user API added to the runtime.

To test, add something like this to an xml course, or make equivalent
 tweaks in mongo.

 <vertical url_name="split_test_vert">
    <split_test url_name="split1" experiment_id="0" condition_id_to_child='{"0": "i4x://MITx/6.00x/html/split_test_cond0", "1": "i4x://MITx/6.00x/html/split_test_cond1"}'>
       <html url_name="split_test_cond0">condition 0</html>
       <html url_name="split_test_cond1">condition 1</html>
    </split_test>
  </vertical>

Also needs an experiment configured in the course policy json: e.g.

        "user_partitions": [{"id": 0,
                                      "name": "Experiment 0",
                                      "description": "Unicorns?",
                                      "version": 1,
                                      "groups": [{"id": 0,
                                                        "name": "group 0",
                                                        "version": 1},
                                                        {"id": 1,
                                                        "name": "group 1",
                                                        "version": 1}]}]

(This particular snippet will work inside a course with org MITx
 and course name 6.00x)

Co-Author: Sarina Canelake <sarina@edx.org>
Co-Author: Julia Hansbrough <julia@edx.org>
Co-Author: Diana Huang <diana@edx.org>
Co-Author: Calen Pennington <cale@edx.org>

[LMS-2095]

Make XBlock client-side runtimes proper classes, so that handlerUrl can
be defined in a per-runtime way, and we can have multiple runtimes on a
single page.

[LMS-1630][LMS-1421][LMS-1517]

fixing unit tests

fixing merge error

fixing xqueue submission issue with unicode url (trial 0.1)

fixing fotmats as commented upon

removing yaml file language selection

Unicode changes to support QRF

removed unnecessary pass in modulestore/init.py

fixing merge error

fixing fotmats as commented upon

removing yaml file language selection

fixing pep8 violations

- fixing pylint violations

pylint violation

fixing line spaces and formats

ignore pylint E1101

remove empty line

fixing pylint violations

 pep8 violations

bulk mail unicode/decode

fix migration error

fix pep8 just to push again

more unicode/decode
Final changes to comments and error messages.

[LMS-1613]

Updates to depend on the latest version of XBlock, which includes
support for service-to-service (thirdparty) handler urls, which aren't
authenticated with a user (unlike handler requests coming from the
xblock client-side javascript).

Co-author: Ned Batchelder <ned@edx.org>

Adds xblock handler_url support to the LMS, and makes handle_ajax use
that code.

[LMS-230] [LMS-229]