Rework drag/drop on overview and subsection pages.

Contains the following things:

1) Indicator (blue arrow and line) showing where the element will be dropped.
2) Dragging an expanded element will first collapse it, then re-expand on drop.
3) Dragging into a collapsed element does NOT expand the element on hover. The item is dropped as the top element in the item ("prepend"), and then the collapsed element is expanded on drop.
4) Scroll up and down should work while dragging an element.
5) Change from "a" links to spans to prevent the default action for an a-link.
6) Delete unused settings_discussions_faculty.html file.
7) Delete now unused hesitate.js file.
8) Re-enabled some of the overview_spec.coffee unit tests that had been removed in the RequireJS checking. However, there are 2 (unrelated to drag and drop) that are still failing in Jenkins, so I have commented them out. Note that overview_spec.coffee was completely deleted in the RequireJS checkin, so it appears as a new file.

@singingwolfboy and @frrrances Please review (including check out branch and try to break it!).