Entity Metadata Wrapper

Added an easy to use wrapper for entity metadata, because it can be hard to understand normally.
The class extends WrappedDataWatcher and adds all methods to get/set the metadata.
This currently works with the SpawnMob class and the SpawnNamedEntity class, but it can be used for all entities in the future.
Users will use this class when normally using WrappedDataWatcher, so it would look like setMetadata(EntityMetadata value);
I did some sample javadoc at the beginning, but it takes so much time to write.  I will finish it if you like the idea.
I am also planning to add enums for different typed (villager, sheep, horse, etc) and even the bit masks for mob flags (right now the class assumes the user know how to bitshift)