Rewrite the audio/video encoding components for BigBlueButton.

I've been working on this for a while, and it's adapted from code that
has been fairly well-tested on a wide variety of recordings. I've found
it to do a more accurate job of combining multiple webcam files, and it
should be more accurate in the audio as well.

Another key feature is that it does fewer re-encoding steps during video
processing, which should both speed it up and hopefully improve quality.
The settings on the VP8 encoder have been tuned somewhat as well.
Add a video quality bump when deskshare videos are present.
Add missing license header to edl.rb
Reset the offset to 0; the new scripts seem to have better sync?
Bump the max difference for audio stretch up to 5%
Update the ffmpeg version check in bbb-conf
Change the background color of the video area to white to match

The new scripts render the videos over white, so you get occasional
black bits sneaking in without this.
Merge pull request #243 from kepstin/recording-rewrite

Recording rewrite