Added a setting to allow -90 degree rotation. Combined with fliph and
flipv, I think this means every one of the 8 major orientations is covered
(2^3). 0, 90, 180, 270 times 2 (mirror image in each rotation). I chose
-90 instead of 90 because that keeps the upper left corner pinned to the
same spot.
The extra ms-transforms aren't for this issue exactly but allowed me to
test my changes in ie. I've tested Chrome, Firefox and IE11. I don't
have Safari handy, but if it breaks it *should* be only when this is
enabled.

on another event handler that may be added elsewhere.