Drag and drop support on the course outline page.
Studio: re-implemeting visual styling for drag and drop:

* adding back in drag and drop indicators to outline DOM
* correcting visual display of drag action in outline UI
* adjusting styling of outline drag and drop indicators
* adjusting styling of drag and drop was-dropped state
Remove is-expanded.
Use outerHeight instead of height.
Move the splint, and make it an li.
Fix up unit tests.
Cleanup.