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

Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar

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

TNL-3179

This reverts commit 42e78463.

This reverts commit 53db053c, reversing
changes made to 386a8a27.

enrollments.

The goal for this PR is to have a single mechanism for registering users and
reducing the number of places where special-casing for ccx courses is needed. The
migration at this point is purposefully limited to convert ccx memberships into
student enrollments when moving forward. No backward migration is in place at the
moment. The ccx membership tables are not removed at this time. It is possible to go
backwards and forwards multiple times with no errors or data loss.

add doc strings; fix pep8 warning
address some minor issues brought up by the code review process

Final official name is Custom Courses for EdX (CCX), rename all code to remove previous name.

Rename the FEATURE constant used to identify this feature

Rename the middleware for the CCX change

rename the constant used for storing the current poc id on the session.

rename the _PocContext threading local

rename the override provider in all places where it is referenced

`PersonalOnlineCoursesOverrideProvider` -> `CustomCoursesForEdxOverrideProvider`

generally rename symbols from overrides.py to replace `poc` with `ccx` where possible without changing model names or attributes

rename more symbols from poc to ccx
rename util functions from app utils module

general symbol renaming poc -> ccx in views.py and related url changes

Rename the coach role wherever it is used.

reword poc_coach to ccx_coach

UI rename

replace POC with CCX globally

template context variable renamed

rename poc_ to ccx_ in urls and all related locations (views, js, scss etc)

remove pocs migrations

Final massive renaming, including models.  Re-built migration.

cleaning up a few tailing references

Fix reference typo in schedule template JS

undo modifications made on the fly in test setup to ensure that our tests are properly isolated from the rest of the system tests.

Fixes jazkarta/edx-platform#38

Clean up some leftover strings and comments

fixing more strings and comments in python files

fix a naming error in the schedule tab that was causing problems in deleting courseware items.

Fixes jazkarta/edx-platform#36

updating tests and utility code to match changes in infrastructure from latest rebase