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).
Would it make more sense to have a PubSub model, or an Event model (with listeners)?  It's almost the same in the implementation, but slightly different to use.  I think I'd prefer an Event model.