Basic Mobile API

This includes OAuth2 support and course video listing support
required for the mobile Video Locker application.

Conflicts:
	cms/envs/common.py
	common/djangoapps/student/models.py
	requirements/edx/github.txt
Comment out course image to help address performance problem on sandbox display of prod course listing.
Switch mobile API to use opaque_keys lib
Remove almost all course information from the course listing in order to avoid timeouts on the front page. Temporary expedient, must be fixed for real before merging to master.
Make the course listing slightly more informative.
Merge branch 'master' into ormsbee/mobile_api2

Conflicts:
	lms/envs/common.py
Merge branch 'ormsbee/mobile_api2'