Add custom CSS and JS for ad-hoc collaboration sub-account

So far, this hides inactive nav items, and removes un-used roles from the roster search filter and the add new users dialog. 

Still need to look at remove SIS ID from certain views. Waiting for Melissa to set up canvas-test's collab space to match production's.

After deploy:
- in /accounts/2/settings, enable option to allow sub-accounts to have custom includes
- in collab space settings, define /sfu/css/collab_space.css and /sfu/js/collab_space.js