Remember the user last thread sort preference
FOR-545
Merge pull request #3738 from mlkwaqas/waqas/for545-user-last-thread-not-remembered

Waqas/for545 user last thread not remembered
Fixes: DOC-599
Merge pull request #4142 from edx/ahodges/documentation/DOC599

Fixes: DOC-599
Add info about Mandarin Chinese option to LMS
Merge pull request #4149 from edx/sylvia/docs/release_notes_6_16

Add info about Mandarin Chinese option to LMS
Tracks last edited date and user, and adds has_changes for blocks.
link to code ownership page from CONTRIBUTING.rst file
Merge pull request #4152 from edx/db/code-ownership

link to code ownership page from CONTRIBUTING.rst file
Merge pull request #4060 from edx/benmcmorran/edit-tracking

Tracks last edited date and user, and adds has_changes for blocks
Fix typos.
Consistent configuration settings for MODULESTORE in both LMS and Studio.

Update all non-test callers to use Mixed modulestore.
Refactor get_parent_locations and users
STUD-1663

Conflicts:
	cms/djangoapps/contentstore/tests/test_contentstore.py
	cms/djangoapps/contentstore/tests/test_crud.py
	cms/djangoapps/contentstore/views/item.py
	cms/djangoapps/models/settings/course_details.py
	common/lib/xmodule/xmodule/modulestore/mongo/base.py
	common/lib/xmodule/xmodule/modulestore/mongo/draft.py
Make XML import/export work.
Getting test_mixed to work
LMS test fixes #1.
Fix mappings
Fix Tests
Fixing test_mixed_ms
Update migration code to not request a specific store.
Fix tests.