cef: install libffmpegsumo.so

fixes #136 

if you want to test this, just add
```html
<video controls="" autoplay="" name="media"><source src="http://video.webmfiles.org/big-buck-bunny_trailer.webm" type="video/webm"></video>
```
to settings.html after <div id="gamesettings">

NOTE: this is a candidate for the stable branch
commit 0552d3aede7d778dee04f317d59305bf18ba760b requires a cef rebuild