auto-migrate old mongo to draft modulestore
Move modulestore django settings migration code down into the modulestore layer so it works for all django-based callers.
reverting back to migrating the settings in the env files
Added deprecation warnings.
Update opaque-keys library
Merge pull request #4380 from edx/nimisha/mongo-bwc-config

auto-migrate old mongo to draft modulestore
Merge pull request #4410 from edx/sarina/update-deprecation-warnings

Update opaque-keys library
split_draft sub class
converge create_item.
Fixed merge conflict in split_migrator.
Fix test failure