Add tests that verify Studio can still render with bad HTML content.
Bok-Choy Video Transcript Tests
Studio: revising %cont-text-sr Sass placeholder based on modern browser support
Studio: breaking longer user/id-based strings on unit and container views

STUD-2113
Fix for "ui-sortable" existing in HTML within HTML module.
Disable JS error test until Andy's PR.
Friendly error if invalid student identifier is entered for due date extension
Merge pull request #4906 from bradenmacdonald/fix-idde-invalid-student

Friendly error if invalid student is entered for due date extension
Merge pull request #4916 from edx/talbs/studio-fix-unitsidebar

Studio: FIX - Unit/Container Sidebar Content Wrapping
Merge pull request #4859 from edx/ammar/bok-choy-video-transcript-tests

Bok-Choy Video Transcript Tests Batch1
Merge pull request #4857 from edx/christina/stud-2093

Add bok choy tests for bad HTML module content.
Replace reference to Google OpenSans with edX-hosted OpenSans
Addressed comments.