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).
And would it make sense to use some open source code, such as https://github.com/mroderick/PubSubJS/blob/master/src/pubsub.js, that may have ironed out cross-browser issues for you?