conversion from package_id to org+offering
Make course_id a required arg to split.create_course
and remove attempt to make it unique. Instead raise exception on dupe.
STUD-1359

Conflicts:
	common/lib/xmodule/xmodule/modulestore/mixed.py
	common/lib/xmodule/xmodule/modulestore/tests/test_orphan.py
Split: add schema version and drop pretty_id (was placeholder looking for purpose)
STUD-1359

Conflicts:
	common/lib/xmodule/xmodule/modulestore/locator.py
	common/lib/xmodule/xmodule/modulestore/tests/test_orphan.py
Generate split test data via split

Conflicts:
	common/lib/xmodule/xmodule/modulestore/tests/test_split_modulestore.py