AppRTC: Add new modules for logging and pubsub.

The logging module will publish an error topic when using Log.error in addition to logging to console. Other interested modules will eventually subscribe to the error topic (e.g. the infobox, which will then display the message).
I was working from the perspective of keeping things simple since this is still demo code. Are we supporting anything other than Chrome/Firefox? I'm not opposed to open source bits, particularly since that one seems to have been measured for perf.