add code to actually go through and delete the draft modules
extend tests to assert that all draft content is cleaned up. Also add assertion that assets are deleted as well
switch from prints to logging.debug. Also refactor some duplicate code
remove unnecessary type check on the module store. XML module stores will throw an exception when deleting an item...
Merge pull request #330 from edx/fix/cdodge/delete-course-delete-drafts

[STUD-380] Fix/cdodge/delete course delete drafts