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

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

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.

TNL 3294 - Prevent double click creating multiple teams

LMS: increasing contrast of footer text

Increasing contrast in gray meta/date text on course dashboard

i18n fix

saleem-latif/SOL-565

Now using withDisabledElement to prevent multiple event handling. I've
attempted to write this as a common function in view_utils, so that this
approach can be used more generally, wherever needed. Includes a unit test.

Thanks to Christina and Andy for all their help on this one.

1. Add missing '_()' in capa_base.py & video_xfields.py
2. Fix a bug in instructor_dashboard.py that causes crash when ANALYTICS_DASHBOARD_NAME contains non-ascii characters.
3. Workaround for mis-extractions inside .underscore files when using gettext along with interpolate.

Improve response handling in AjaxHelpers

I've changed the logic so that AjaxHelpers keeps
track of which requests have not yet had mock
responses sent. This ensures that every response
is handled before moving on to the next one,
rather than always handling the last request.
My intention is that this won't allow bugs to creep
in where a request isn't fired and instead the test
responds to an old request. It also should ensure
that extra events aren't accidentally fired.

Improve team testing of routers

Remove "responsive" check before deciding whether to add a viewport tag.