Lots of refactoring.
Refactored gradebook format to no longer have categories. Now the gradebook
only has assignment and auxillary groups.
Refactored the problem edit views to use shorter URLS
Refactored so that creation of file storage is no longer lazy. This should help
reduce the possiblity of race conditions because it is less likely for two
admins to create the same course at the same time.
Fixed the bug where renaming a course would cause it to lose all submissions.