Rewrote course adding and dropping to be able to handle a list of courses--to work it currently uses a hardcoded list with one course in it. In addition broke out utility methods into helpers.py. Withink helpers (and elsewhere where appropriate) created a local variable 'url' to allow for easy switching between sandbox and staging applications. As of commit, all 55 steps pass.

Feature/arjun/course specific css

Added optional <wiki> tag to course to specify an alternative wiki page.

Feature/bridger/new wiki

Separate caches per-domain-name

Conflicts:
	lms/templates/wiki/settings.html

Fix for 500 on showanswer for choiceresponse

Catch errors in module load

Feature/tomg/fall design

* if error is in xmodule_constructor(), catch and return an ErrorModule
* if error is somewhere else in get_module(), return None

Fixed syllabus to look good with new courseware styling

Added django-wiki's requirements to requirements.txt, because they weren't being included automatically.