Changes:
* Added a base layer class which can intelligently switch between pony and human.
* Skins no longer are "converted" when they are already in the new format.
* Illagers now use the existing model and texture format.
* Metadata can now be read from the .mcmeta file (taken from old illagers)
* Non-converted resources are no longer re-uploaded
* (1.12) Parrots are rendered on the head instead of shoulders
