TE-489

First step in moving assets out of the contentstore (optionally).
https://openedx.atlassian.net/browse/PLAT-77

PLAT-104

PLAT-104

This commit makes the following changes:
1. If there are syntactic errors in the Range header, it is ignored and
the full content is returned. This conforms to the spec.
2. In case of multiple ranges in the header, the full content is returned.
This behavior differs from the spec which says that a multipart response
should be returned.

PLAT-104

Currently, users can only download ContentStore files from first byte to
last byte.

With this change, when a request to the ContentStore includes the HTTP
"Range" parameter, it is parsed and StaticContentStream will stream the
requested bytes.

This change makes possible to stream video files (.mp4 especially) from
the ContentStore. Users can now seek a specific time in the video
without loading all the file.

This is useful for courses with a limited number of students that
doesn't require a dedicated video server.

Conflicts:
	cms/djangoapps/contentstore/views/tests/test_container_page.py
	common/djangoapps/external_auth/tests/test_shib.py
	common/djangoapps/student/tests/test_login.py
	common/lib/xmodule/xmodule/modulestore/tests/django_utils.py
	common/lib/xmodule/xmodule/modulestore/tests/factories.py
	common/lib/xmodule/xmodule/modulestore/xml_importer.py
	lms/djangoapps/branding/tests.py
	lms/djangoapps/courseware/tests/test_submitting_problems.py
	lms/djangoapps/courseware/tests/test_video_handlers.py
	lms/djangoapps/instructor_task/tests/test_base.py
	lms/djangoapps/instructor_task/tests/test_integration.py

LMS-2876

Refactor get_parent_locations STUD-1663

LMS-2801

[LMS-2757]

This commit updates common/djangoapps.

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]

This reverts commit a517dc20.

This reverts commit ec01253e, reversing
changes made to ae8c9710.

as a first step to separating db connection from modeling
and to support location mapper and contentstore using same db config as modulestore

   And include Don's fix for partial course_id lookup.

        Includes static server tests.

support uploading and referencing assets as streams rather than having to read everything into memory first

change from throwing a Http404 exception, which I believe will try to render a static 404.html template - and ironically triggers a 500 server error. Just create a HttpResponse and set the status_code to 404.

refactor StaticContent id scheme to be the same as moduledata. Also expose a new 'get all content for course' which will be needed to support a asset management page.

per feedback, use reverse() when generating callback urls. Also generate thumbnails when ingesting static images. We'll need these handy for the CMS UI.

Support asset library references in CapaModule. Also some code refactoring/cleanup. Preparing for review and submit