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.
For new math, drop the plain text option.

This fixes #420.

Conflicts:

	src/plugins/oer/math/lib/math-plugin.coffee
	src/plugins/oer/math/lib/math-plugin.js
Move base into ownmacro/slot, make other urls relative

There is now only one absolute url left. Unfortunately base tags
cannot take relative paths. We can hack this using JS.
Merge branch 'oerpub-ticket189-refix' into testing

Conflicts:
	src/plugins/oer/popover/lib/popover-plugin.js
Merge branch 'oerpub-ticket420-pull' into testing
Merge branch 'oerpub-ticket372-pull' into testing