Add video annotation support

This work is still work in progress, doesn't seem to work for http://acroeng.adobe.com/Test_Files/classic_multimedia//VolvoS40V50-Full.pdf

It does seem like it worked in the beginning, but doesn't seem to work for me.  

Rebasing change from pull request #4376 to get some reviews and pitfalls. 
I see. How about:

````
var canPlayType = element.canPlayType(contentType);
if (!canPlayType && contentType in navigator.mimeTypes) {
   // Use <object>
} else if (canPlayType) {
   // Assume "maybe" or "probably"
   // Use <video>
} else {
   // Show link?
}
```