Convert component.py to use RESTful URLs.

STUD-844

Things to test:
1) On unit page, switch between public and private. Test creating and deleting drafts. Preview draft content and also check View Live.
2) Do edit operations on the subsection view page.
3) Do edit operations on the unit view page.
4) Creation of new units (both on the course overview and subsection view pages.

@dmitchell Please review. I recommend ?w=1 for component.py review.