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)
rename to match module? or rename the file `tech-order` to player priority. Odd to make an alias i think.