Change partitions logic to include partitions with one deleted group

This reverts commit f97f0525, reversing
changes made to 800bcd8e.

This reverts commit 1224e341. I've also added
NotImplementedPartitionScheme, which allows deprecated partition types to have
a valid entry point despite being unusable.

TNL-6675

TNL-6746

TNL-6744

TNL-6674

This reverts commit 83f2be49, reversing
changes made to 01ed1742.

This is unused, and will no longer be supported on edx.org. Also adds a
DeprecatedModel utility class.

TNL-6126

HOSTNAME_MODULESTORE_DEFAULT_MAPPINGS,

* Automatically create user partitions on course publish for each ICRV checkpoint.
* Disable partitions for ICRV checkpoints that have been deleted.
* Skip partitions that have been disabled when checking access.
* Add verification access control UI to visibility settings.
* Add verification access control UI to sequential and vertical settings.
* Add partition scheme for verification partition groups.
* Cache information used by verification partition scheme and invalidate the cache on update.
* Add location parameter to UserPartition so the partition scheme can find the associated checkpoint.
* Refactor GroupConfiguration to allow multiple user partitions.
* Add special messaging to ICRV for students in the honor track.

Authors: Zubair Arbi, Awais Qureshi, Aamir Khan, Will Daly

TNL-2435

force save "download_video" field if not set

set timezone to UTC explicitly

Cannot create an xblock in a course that doesn't exist.

make_asset_key does not start with "/" for split locators.

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]

TNL-652

Refactor all callers (often replacing with more appropriate fn)

Also, added for_branch_setting method to old mongo and removed some
branch verification tests

Conflicts:
	common/lib/xmodule/xmodule/modulestore/mongo/draft.py
	common/lib/xmodule/xmodule/modulestore/split_mongo/split_draft.py
	common/lib/xmodule/xmodule/modulestore/xml_importer.py

STUD-1873

STUD-1875

[LMS-2757]