Revert "SUST-35 Implementation of course_key_from_string_or_404 to return course_key or raise a 404"

Revert "SUST-35 Implementation of course_key_from_string_or_404 to return course_key or raise a 404"

-Updated method "course_key_from_string_or_404" to raise message too.
-Wrote tests for "course_key_from_string_or_404" when exception message is given.
-Modified existing methods to use "ddt.data".
-Used Splunk logs to find exectly where we were getting "Invalid Key Error"
-Updated Views where we were getting "Invalid Key Error" in splunk logs.
-Wrote tests for those View End points where we were getting "Invalid Key Error"

Converted lettuce Course Team page tests to bok choy

- has_course_access renamed to has_course_author_access for clarity
- Changed doc string to clearly state that it determines whether or not
  a user has write access to a course

[LMS-2757]

This commit adds all of cms.

These keys are now objects with a limited interface, and the particular
internal representation is managed by the data storage layer (the
modulestore).

For the LMS, there should be no outward-facing changes to the system.
The keys are, for now, a change to internal representation only. For
Studio, the new serialized form of the keys is used in urls, to allow
for further migration in the future.

Co-Author: Andy Armstrong <andya@edx.org>
Co-Author: Christina Roberts <christina@edx.org>
Co-Author: David Baumgold <db@edx.org>
Co-Author: Diana Huang <dkh@edx.org>
Co-Author: Don Mitchell <dmitchell@edx.org>
Co-Author: Julia Hansbrough <julia@edx.org>
Co-Author: Nimisha Asthagiri <nasthagiri@edx.org>
Co-Author: Sarina Canelake <sarina@edx.org>

[LMS-2370]

STUD-1006

on new Locators to make it clear that they have a different syntax
than Location.course_id altho they represent the same info.

usage_id implies self-sufficiency. The block_id is relative to its structure.

Ensure user admin screen gets the union of all possibly matching group names.
Smarter default group naming.
STUD-1003

Move index access into the url
Move course creation into the url
Add helper methods for testing to serialize json data and set accept header.

Move RESTful URLs into our "done" section.

Pattern for how to do refactoring from locations to locators and from
old style urls to restful ones.

Features coming down the pipe will want to be able to:
* Refer to enrollments before they are actually activated (approval step).
* See what courses a user used to be enrolled in for when they re-enroll in
  the same course, or a different run of that course.
* Have different "modes" of enrolling in a course, representing things like
  honor certificate enrollment, auditing (no certs), etc.

This change adds an is_active flag and mode (with default being "honor").
The commit is only as large as it is because many parts of the codebase were
manipulating enrollments by adding and removing CourseEnrollment objects
directly. It was necessary to create classmethods on CourseEnrollment to
encapsulate this functionality and then port everything over to using them.

The migration to add columns has been tested on a prod replica, and seems to be
fine for running on a live system with single digit millions of rows of
enrollments.

Remove _

Minor cleanup.

When Chrome sends the AJAX request to add a user to the course team, it sets the
Content-type to "application/json". However, when Firefox sends the same request,
it sets the Content-type to "application/json; charset=UTF-8". This commit only
checks that the Content-type begins with "application/json", not is identical
to it; that way, Firefox can play, too.

STUD-554

Code review feedback.

When Chrome sends the AJAX request to add a user to the course team, it sets the
Content-type to "application/json". However, when Firefox sends the same request,
it sets the Content-type to "application/json; charset=UTF-8". This commit only
checks that the Content-type begins with "application/json", not is identical
to it; that way, Firefox can play, too.

They contain too much incorrect permission checking