for backward compatibility reasons, IE11 sets both msPointerEnabled and
pointerEnabled. Changed the order for the test and added 'else if' to
not duplicate handlers on pointer events

Added unprefixed touch-action CSS attribute
Added unprefixed pointer events handlers hooks

Added un-prefixed touch-action CSS attribute
added un-prefixed PointerEvents event handler hooks

use 'url()'-free path when specifying parallax image, refactor so that parallax is applied to background class, remove unused attributes #595

This prevents the upcoming slide on the notes page from triggering
slidechanged events.  I believe this fixes issue 578, as well.

Fixed problem with parallax background  not working under FF