Refactor split migrator

LMS-2936

Removed a bunch of loc_mapper code
Cleaned up offering now being course and run in a few places
Removed extra db queries

Conflicts:
	common/lib/xmodule/xmodule/modulestore/tests/test_publish.py
OK I get it, just confusing as no docstrings anywhere. In compare_courses, the third argument "published" is to be a Boolean. Would recommend more docstrings and comments this is hard if you guys ever decide to leave edX.