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).
What do you prefer about the Event model in particular? I went with pubsub primarily for readability.

With Event model we'd be making each module encapsulate or inherit from an event emitter base class. Another way of putting it, pubsub stores subscriptions globally whereas event stores subscriptions per object. I think it's simpler to avoid inheritance for sample code, but you're right that Event makes more sense form the viewpoint of we don't expect to have multiple publishers for the same topic.