Channel buffering

Hey Ben,

I'm not 100% sure if this is the problem or not, but I'm probably about 95% sure it is.  There is currently a recommended max payload size of 16K (see Chrome 32 webrtc release notes - https://groups.google.com/forum/#!topic/discuss-webrtc/AefA5Pg_xIU) and I try to address that with the `rtc-bufferedchannel` module.  It's still a work in progress but for the most part I think I've taken care of things there.

One thing I was noticing during my debugging though is that Firefox 26 seemed to not trigger the `mySnapshotURIChanged` polymer attribute change event (note the additional console log statement), but testing under Firefox 27 was completely different and it I got interop between FF 27 and Chrome 32 pretty much straight away.  I'm not sure why this would be the case (I don't know enough about polymer), but I'm going to dig a bit further to make sure it's not `rtc-videoproc` or something else causing the problem.

Cheers,
Damon.