Reworked the command registration system

Please read the [javadoc](https://github.com/Limeth/Terasology/blob/16965803d4edd128ce5baaa3c35e814de26752f3/engine/src/main/java/org/terasology/logic/console/Command.java).
Is there a reason this isn't ','? Would it work with ','? It seem to me that ideally a user shouldn't need to know varargs are involved, and shouldn't have to use a different deliminator where they are involved.