The existing pattern of using `override_settings(MODULESTORE=...)` prevented
us from having more than one layer of subclassing in modulestore tests.

In a structure like:

    @override_settings(MODULESTORE=store_a)
    class BaseTestCase(ModuleStoreTestCase):
        def setUp(self):
            # use store

    @override_settings(MODULESTORE=store_b)
    class ChildTestCase(BaseTestCase):
        def setUp(self):
            # use store

In this case, the store actions performed in `BaseTestCase` on behalf of
`ChildTestCase` would still use `store_a`, even though the `ChildTestCase`
had specified to use `store_b`. This is because the `override_settings`
decorator would be the innermost wrapper around the `BaseTestCase.setUp` method,
no matter what `ChildTestCase` does.

To remedy this, we move the call to `override_settings` into the
`ModuleStoreTestCase.setUp` method, and use a cleanup to remove the override.
Subclasses can just defined the `MODULESTORE` class attribute to specify which
modulestore to use _for the entire `setUp` chain_.

[PLAT-419]

Move modulestore config for tests to an importable location
Disable pylnt warning for lms imports in common tests
Refactor all testcases that loaded all xml courses
TE-610
TE-489

TE-489

[LMS-2757]

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]

In the current implementation if the path prefix contains the
wiki_path value it gets deleted. For example if the prefix is
'/courses/edx/math101/2014' and wiki_path is '101/' the final
prefix becomes '/courses/edx/math2014'.

LMS-2556

remove unnecessary code, and clarify what it's doing.

wiki middleware fix (LMS-2461)

CourseRole names have a new format (type_org.number.run). Previously
when checking if a user was staff for a course wiki type_org/number/run
and type_number format role names were checked by parsing user group names.

This logic has been refactored to first fetch all courses which use the
particular wiki_slug and then use courseware.access.has_access to check if the
user has staff permissions on any of the courses.

LMS-2136

STUD-1006

All the dialogs in the wiki are now accessible to screen readers.

Also, the "Switch to selected version" button did the odd thing of
reloading the page with the new version selected, but inside a dialog.
That is now fixed.

The merge dialog has a warning that looks kind of funky still, but you
can read it, unlike the previous code.

LMS-1337

This centralizes the logic for group membership, and means that we
don't need to make queries to find out whether the legacy groups names exist.

LMS-1355

LMS-1307

Modified navigation tests to use MixedModulestore
Updated factories to find editable modulestore

Updated test_submitting_problems

Updated test_tabs.py

Updated test_view_authentication

Updated test_views

Updated courseware/tests/tests.py

Updated test_masquerade

Updated test_module_render

Pylint fixes

Updated video and word cloud tests

Updated course wiki tests

Updated license and open_ended tests.
One open_ended test still failing due to Mako initialization issues

Updated staticbook

Updated django_comment_client tests

Updated instructor tests

Updated instructor task tests

Updated external_auth tests

Updated course_groups