Refactoring of code that prevents popup closing

This uses the fact that aloha won't deacivate the editor if it has
.aloha in its hierarchy. Of course marking something with class=aloha
brings about styling baggage, so that had to be reset.
Append popovers to the body of the document instead.

This moves the popover out of the editor area, which means mouse clicks and
keypresses does not cause selection-change events in your editor. Unfortunately
this only works with bootstrap>=2.3, but at the moment it is not broken for
oerpub so this is an acceptable outcome.
Mark click events with preventDefault

This indicates to higher level event handlers that the link plugin has already
handled the click event. Specifically, it prevents github-book from opening it.
Merge branch 'ghbook-ticket455' into testing

Conflicts:
	src/plugins/oer/popover/lib/popover-plugin.coffee
	src/plugins/oer/popover/lib/popover-plugin.js