Fixed youtube id lookup (no longer storing youtube urls in db)

Lookup youtube videos by id

Make the admin more usable.

Authorization changes to tighten permissions and use OAuth2.

1. Explicitly added OAuth2 and Session as the authentication types
allowed. Django Rest Framework allows the use of defaults via
settings, but this may have unwanted side-effects since there are
others using DRF with different APIs that have different requirements.

2. Created a ReadRestrictedDjangoModelPermissions class that is a
subclass of DjangoModelPermissions. DjangoModelPermissions only cares
about edit/update/delete permissions and makes everything world
readable by default, which is not desirable for this API.

3. Added the DRF login URLs for running this project locally.

4. Add edX fork of django-oauth2-provider to requirements.

Changed name of model CourseVideos -> CourseVideo.

Django model names should be singular.

URL change: /video -> /videos, added /admin

Changed the resource URLs to be plural for consistency with other
services in edx-platform. Added /admin for standalone running with
"manage.py runserver". Instead of using edxval.urls directly,
runserver now uses a top level urls.py that includes edxval.urls
as well as the debug toolbar and admin.

Switch to using migrations.

Using an older version of migrations to match edx-platform.

Support youtube encoded videos by using a different Profile.

Version conflict with another edx-platform dependency.

Use the correct course_id regex.

Expose course_id to the API

Rest Framework 2.4 requires request for serializers.HyperlinkedModelSerializer

Add authentication and model permission checking to REST API.