Added support for Youtube and Vimeo videos.

I pulled together the code for embedding youtube video from @puredistortion and added Vimeo support. I also corrected some BS3 specific events for modal windows. You're welcome to port this code to BS2 also and improve the JS code where needed.

Inspired from https://github.com/puredistortion/bootstrap-wysihtml5/commit/7e2c149dd2a3b6f416dae97d79c4d585eae7a7e9