Bug 1071009 - [Loop] Expose bitrate, frames dropped and frame delay to a...

...pplications via TB library.
Added all information given by tokbox including framerate on encoder/decoder side, frames dropped and bitrate. RTP information also available.
Tokbox doesn't provide framedelay information. That info must be retrieved from gecko.
this code is not necessary, please see comment https://github.com/mozilla-b2g/firefoxos-loop-client/pull/340/files#r21078223