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).
I'd feel guilty if I hardcoded the array delimiter to ',', so I added this field. The reason the parameter delimiter isn't a space is, that having to type quotes might not always be pleasant. So instead of typing:
*tell "Limeth Immortius" Hello, World!*
they can type:
*tell Limeth,Immortius Hello, World!