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.
Lots of tightening and fixing for making mixed
the routing but not necessary intermediate.
Fixes to start Studio.
Remove TEST_MODULESTORE settings override
it was obsolete
Fixed test_item.py.
More test fixes
 #Fix test_sysadmin.py.

Fix LMS and CMS acceptance and unit tests.
Clean up the semantics of delete_item

more fixups
Implement has_item in draft.py.

Fix test_courses.py.

renamed revision values.

fixing clone

Fix prefetching test.

Fix more LMS acceptance failures.