Move oauth_dispatch from lms to openedx/core.

- Using jwt_decode_handler from edx-drf-extensions
- Updated djangorestframework-jwt
- Removed feature flag around JWT auth

ECOM-4221

ECOM-4013

Available backends:

* django-oauth-toolkit (DOT)
* django-oauth2-provider (DOP)

* Use provided client ID to select backend for
  * AccessToken requests
  * third party auth-token exchange
* Create adapters to isolate library-dependent functionality
* Handle django-oauth-toolkit tokens in edX DRF authenticator class

MA-1998
MA-2000

This will leverage the nose attrib plugin to allow us
to break tests apart on our build system to run
in parallel on separate nodes.

Modified how the per object permissions are enforced in the CCX REST APIs

ECOM-3419

CCX REST APIs
OAUTH2 authorization for CCX APIs
- oauth2 authorization required for ccx list.
- Course-instructor permission for ccx api endpoint
- Protection for detail view too.

Tests for CCX REST APIs and OAUTH2 authorization

This reverts commit 46df4545, reversing
changes made to 039e6cdf.

ECOM-3384

ECOM-3419

Format responses as a JSON dict containing an error_code and a
developer_message.  user_message is not necessary, as these are API
level errors, not seen by end users.

MA-1900

The permissions class now supports non-GET requests.

ECOM-2893

- The permission now checks the correct request attribute (GET instead of data).
- The Credit API view test has been updated to check for the positive access instead of just denial.

 ECOM-3096

* Catalog results are now paginated
* Implements the new namespaced pagination described at
  https://openedx.atlassian.net/wiki/pages/viewpage.action?pageId=47481813
* API level code returns pythonic business objects
* View layer performs serialize at the view layer
* Convert views to use DRF generic views
* Removes an unintentional authentication decorator that caused
  the detail endpoint to return a 401 for anonymous users

MA-1724

- API built atop Django REST Framework
- Added support for OAuth 2.0 and session authentication
- Added permissions around eligibility data

ECOM-2609

Also remove useless docstrings where they were added to keep pylint
quiet.

MA-1416

Created a TypedFileUploadParser that validates the mimetype and then
takes the content and puts it on request.FILES['file'].  Subclasses the
existing FileUploadParser.

Use namedtuple in IMAGE_TYPES as per style guide:
https://github.com/edx/edx-platform/wiki/Python-Guidelines#classes-vs-dictionaries

* Fix paver violations to stablize edx-lint update
* Parens, Line2Long
* Fix missing docstrings
* Fix PEP8 issues
* Address PR feedback (thanks @nedbat!)

TNL-3442