Added fixtures for course and xblock creation
Added bok-choy Studio tests
Added bok-choy tests for ora self- and ai- assessment
Refactored auto-auth; added staff and course-enrollment options
Removed extra javascript properties from page objects

Refactor instructor dash acceptance tests.
Add additional acceptance tests for buttons on 'Data Download' tab.

LMS-58

Fixed grading tests

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.

Instead, we use XModule field default values when creating an empty
XModule. Driven by this use case, we also allow for XModules to be
created in memory without being persisted to the database at all. This
necessitates a change to the Modulestore api, replacing clone_item with
create_draft and save_xmodule.

test.py was changed such that the database being used is test_xcontent
course_helpers.clear_courses now calls contentstore().fs_files.drop() such that all content is removed and the databse is started afresh in the same manner as the modulestore

until it acquires a valid session.

* Missing docstring
* Redefining name from outer scope

for common ui manipulations

rather than using the login dialog.