Refactor videojs tech priority assumption

This refactors how we choose the default videojs tech ordering based on a more robust assumption if the current UA can actually play the video sources in an HTML5 video element. If not we default back to flash first.

/cc @rich-nguyen @gklopper 

(p.s Needs testing in older Firefox's before I attempt to merge)
also this is still the global videojs options object that you are manipulating, it just so happens that you keep rewriting it so it will work. Is it possible to pass the options through to `createVideoPlayer`?