Adding a reviews page to the course and updating the reviews module on the course about page. Removed the existing coursetalk implementation and put it in a fragment, removed the tests as well. Added configuration settings to specify the reviews template as well as the reviews provider. This is all protected by a waffle flag.

Move tests to one test class

Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar

Adds an /xdomain_proxy.html endpoint that serves
the proxy file from the xdomain library.  This
allows IE9 users to iframe in the proxy page
to simulate a cross-domain request with cookies.

Also hooks up the granted and deny events to the course creator group.