Refactored CharacterIds into an an enum

[master-lincoln]

This replaces the use of some int constants in Art to an enum containing all characters. Only when saving and in network packets I use these constants (now the ordinals of the entry in the enum, I kept the order)

[danielduner]

You could explicitly give each character a number, using an Enum constructor:
http://docs.oracle.com/javase/tutorial/java/javaOO/enum.html

[master-lincoln]

Yes I know...but I thought this would be overcomplicated since we already have the ordinals anyway...

But I thought about using an enum constructor for giving each character a sex (for the scream when falling) ie male/female
Added a TODO at the appropriate place