adding a little ux to the download video and transcript links
a11y adjustment to new video and transcript links styles
Tie the USE_I18N setting to DEBUG setting

We want USE_I18N to be on in development, but off in production. Tying
this setting to the DEBUG setting accomplishes that neatly.
Don't remove course update when clicking outside modal.

Fixes bug STUD-822.
Rework course overview drag and drop.

Failed drags bring the element back to where it started; elements are
locked to the y-axis, states are represented as CSS classes for
styling, elements can be dragged across section/subsection borders,
and dragging to the top/bottom of a section Just Works™.

Needs some styling love to give visual representation of where the
dragged element will drop, though.

TODO: It'd be good to have auto expand/collapse for subsections.
Add auto-expand to overview lists.
Make all of section/subsection/unit draggable.
CSS classes for drop targets.
Address PR comments.

Remove unused variables; some changes to match existing BDD spec for
drag/drop (expand-on-hover timeout and dropping with mouse outside of
element); bugfix for section expand; some code cleanup; update and
re-enable acceptance test.
Fix not being able to expand an empty subsection.
Jasmine tests for drag/drop.
Adds in minimally revised drag and drop styling.

Add CSS classes and fix drop destination bug.
Cleanup to drag and drop implementation.

Also includes RequireJS changes.

Fixes bugs:
STUD-755, STUD-152, STUD-700, STUD-699
Comment out tests that fail in Jenkins.
Use wait_for to allow course image time to update
Disable non-deterministic video caption test to get stability on master
Remove unnecessary call from wordcloud test
re-enable some buttons on instr dash
Use assertIsInstance.
Use assertIsInstance instead of assertTrue(type(x) == y)