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).
kill and teleport are Player commands (commands that you only can do as a player with a character).

debugTarget and setWorldTime are more debug commands, I think there may be an existing debug system to throw them into?