make SplitMigrator take a User object, rather than a user ID
first pass on a migrate_to_split Django command
Add some dummy arg parsing tests
happy path unit test
Can't use UserFactory in CMS tests :(
fix test failures: clear loc_mapper cache
move user-finding logic out of command
Added command to delete split-mongo course
Don't cache falsy values
fix pep8/pylint issues
check for old mongo course
fix docstrings
Add test for specifying locator to migrate_to_split command