Refix issue #189 and #172.

Popover is only repositioned on a context change event, not by some
a frequently firing timer event.

Conflicts:

	src/plugins/oer/popover/lib/popover-plugin.coffee
Improve placement logic

Previous logic would drop the popover to the bottom if it fell off the top
or the left. The new code only moves it to the right if it drops off the left,
leaving it at the top. In addition, it drops it to the bottom if it will drop
off the top of the editor, thereby not placing it over the toolbar, at least
initially.
Merge branch 'master' into oerpub-ticket189-refix

Conflicts:
	src/plugins/oer/popover/lib/popover-plugin.coffee
only consider bottom relocation for top located popovers

Without this check, left and right located popovers that are slightly too
wide are relocated to the bottom. Not what we intended.
Merge branch 'master' into oerpub-ticket189-refix

Conflicts:
	src/plugins/oer/popover/lib/popover-plugin.js
Merge pull request #9 from oerpub/oerpub-ticket189-refix

Refix issue #189 and #172.