Moved DIRECT_ONLY_CATEGORIES from mongo/base.py

Added update_item, create_item, create_child to split_draft.py

Cleaned up TODOs in test_mixed_modulestore.py

Unit test for auto-publish

LMS-11017

Added tests to test_mixed_modulestore.py for has_changes and added black_list to _auto_publish

Moved DIRECT_ONLY_CATEGORIES to draft_and_publish.py

Deleted test_split_draft_modulestore.py