basic implementation of enhancement request from issue #3
managed to get a more complete, though hacky, implementation of #3.  the big sticky point was how firefox and safari beahved when switching between applications when already in full screen mode. because we didnt have an event listener for fullscreenchange, and because those browsers released full screen on application or window change (think alt+tab or cmd+tab), you would come back to a empty document.  more work left here to make this worth merging into master
reverting a couple changes to core openseadragon options unrelated to issue #3 . will explore these in #4 were they have already been referenced.
removing unneccessary if
better encapsulation of native fullscreen api
addressing venturo's review notes