Moving the Jabber widget to its own iframe allows us to pop it out
and in of the courseware. Refactoring more of the code (static
assets, templates, etc.) keeps the Jabber app more self-contained
so that it doesn't clutter up the main repo code.

This code needs some Jasmine tests and view tests. It also needs
some extra configuration in the settings and URLs files, namely:

* Must add jabber/templates to MAKO_TEMPLATES
* Must add jabber/static to STATICFILES_DIRS
* Must add route for ?P<course_id>/chat to lms/urls.py

Move Candy.js static assets to Jabber app

Refactor the Candy.js static assets to the Jabber app to keep them
out of the main codebase. This will help modularize the chat widget
so that it's easier to just not include it by default, if desired.

Move registered_for_course out of courseware.views

The Jabber app needs to use this function, and it seems more fitting
to import the function from a non-view module, like the courses
module. So move that function there, and update imports and tests
appropriately.