Also renamed some variables to make them more distinguishable

Replaced the previous method of getting it from HTTP_POST to use
django's mechanism, which may or may not use HTTP_HOST. However if an
attacker changes the request header, there is not much he can do since
he cannot recreate the association nonce.

Add styling for code grader responses

Make collapsibles not collapse the entire page

- need to set text of the link, not the document
- there was something funny with the operator precedence in the ternary operator (was getting 'true', instead of a string)

Kimth/js refactor

fix a bug: can_load() should check for the 'load' permission.

- triggered by anon users when all courses have started (or start dates are off).

Feature/victor/status banner

Don't ignore .py files in static files dirs

- still needs style
- will cache for 10 seconds

Feature/cdodge/cms permissions management

add distinct 'admin' role separate from 'editors'. Only 'admins' should be able to add/remove editors.

fixed custom tab box-sizing glitch in firefox

Renamed jsloader to match up with the content more explicitly; refactored Collapsible out into its own library

make codemirror use visible tabs

added moderator label styles

Fix to update the max_grade cache on StudentModule

* this may not be optimal (compared to e.g. replacing tabs with spaces), but it's a lot better than mystery 'bad indentation' errors

Feature/bridger/course grading