Added a simple IMC handler.

Added a simple yet efficient method of handling IMC messages received by EE3. It can hold 16 different messages by default, but can be extended to more. Handling IMC messages is very easy, by extending IMCMessageHandler and adding it to your map. This would be very useful for a modded that wants to add simple EMC Values, although it is capable of much more. A test implementation is included to show how to extend IMCMessageHandler.