Added pubsub for inter-module communication pattern.

Using a jQuery plugin version of pubsub.

Use $.publish("nameOfEventToPublish", [optionalParametersToPass]) to publish a new event
Use $.subscribe("nameOfEventToSubscribeTo", function(parametersToRead) { Code here }) to subscribe
to an event

Updated error module to subscribe to different error publications
Updated error module to publish a halt event when a critical error is posted
Updated engine to respond to a Halt event (mainly used by the critical error method)
Updated engine to publish the engine tick
Updated sprite submodule to subscribe to the engine tick
Updated sprite submodule to publish a critical error when the tick is invalid during getNextFrame() call