Merge patch/2015-09-22 (Django rest framework) to master

SOL-1190: line breaks in signatory title are not reflected in the cert

reverting the changes sent in PR#9925

Revert "Merge DRF 3.1 in to master"

Merge DRF 3.1 in to master

Preserve DRF v2 behavior of defaulting to None
for missing keys in the grading policy dictionary.

* Upgrade edx-submissions
* Upgrade edx-ora2
* Upgrade edx-val
* Upgrade edx-proctoring
* Update all edx-platform code that depends on DRF, including:
  - auth_exchange
  - cors_csrf
  - embargo
  - enrollment
  - util
  - commerce
  - course_structure
  - discussion_api
  - mobile_api
  - notifier_api
  - teams
  - credit
  - profile_images
  - user_api
  - lib/api (OAuth2 and pagination)

bump version of edx-proctoring to 0.9.11

Patch: Upgrade djangorestframework to v3.1

Merging hotfix 2015-09-24 back in to master

SOL-1189: when a signature image file is uploaded, the preview image looks distorted

MAYN-131: Update Unsupported Browser message

Discussion post cleanup (in preparation for post author images support)

Prevent publish orphans

edx-procoting will be passing back which font-awesome icon to use

Preserve DRF v2 behavior of defaulting to None
for missing keys in the grading policy dictionary.

* Upgrade edx-submissions
* Upgrade edx-ora2
* Upgrade edx-val
* Upgrade edx-proctoring
* Update all edx-platform code that depends on DRF, including:
  - auth_exchange
  - cors_csrf
  - embargo
  - enrollment
  - util
  - commerce
  - course_structure
  - discussion_api
  - mobile_api
  - notifier_api
  - teams
  - credit
  - profile_images
  - user_api
  - lib/api (OAuth2 and pagination)

Manage focus on delete component modal

Initial implementation of API for listing a user's third party auth providers

LMS: replacing proctoring markup from accordion

Update Sinon library

Add main index api doc label for inter sphinx

Addressing contrast and hover states for 'clear filters' button on the find courses page

Use correct reports for jshint diff-quality.

TE-1042 include diff-cover for js.