Merged two multiple-choice-like response types into a single response; created inputtypes for checkboxes and radio buttons adn cleaned up the code a bit. Fixed checkbox responses.

minor patch to fix optioninput; merging this in now, to unblock berkeley's changes to MC; passes my tests.

CodeResponse restricted to only one answer field

Kimth/lms coderesponse

fixed the bug that you can enroll a course several times

Minor bug fix. Properly handles script tags where there are spaces before closing brace. 
Code is also more elegant than original. 
Note that this is not a security bug, as the fix indicated. 

Course start

Conflicts:
	common/djangoapps/student/views.py

edX caching

Dormsbee/portal display tweaks

Changed check_course from a decorator to a regular function that throws exceptions. Much easier to understand now.

Use Course.number, remove final exam and content length from the course sidebar (do we have that data yet?)