Implement a Studio tab plugin manager, define a namespace for Studio tab plugins, and introduce an abstract base class used to represent Studio tabs. This does not introduce changes required to inject such plugins into the Studio UI. ECOM-2187.

mattdrayer/increment-edx-lint: Bump to v0.2.9

asadiqbal08/SOL-1288 Add view of Certs generated to the Instructor Dashboard

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

SOL-1297: Remove platform name from error message in Certificates Web View

SOL-1317: check MILESTONES_APP also when checking prerequisite courses enabled

saleem-latif/SOL-1257: Resetting student history for Entrance Exam on instructor dashboard

Remove unused specs

These have been commented-out for more than 2 and a half years;
I can't think of a legitimate reason for keeping them around at this
point.

These were originally commented out here in
47409654

Make HTML for non-editable views on leaner profile page more logical

remove link style, add pointer, adjust spacing on profile

saleem-latif/SOL-1266: Move Course Number and Course Number Override below Course Title section

Fixed pylint violation for files in lms/djangoapps/ccx

TNL-3297

Update translations (autogenerated message)

Fixed pylint violation for files in lms/djangoapps/certificates

Make these tests more unique for multiprocessing.

Update Credit Requirement Status Table for Skips

saleem-latif/SOL-1297: updated message for 500 error on certificate preview

Clean up of common JS specs using RequireJS.

The test was not running where it lived before.

ziafazal/SOL-1254: Student should see rest of courseware as soon as Entrance Exam is passed

ECOM-2551

Fixed pylint violations for files in lms/

Fixed pylint violation for files in lms/djangoapps/bulk_email

Fixed pylint violations for files in lms/djangoapps/branding

mattdrayer/update-gencert-modes: Added prof-ed modes to set