add animations collection to TextureAtlas
use separate Animation class for now to hold info. new addAnimation method. TextureAtlasAnimator will read through these and set up it's own data structures from them
add method to register/copy all animations from a TextureAtlas at once
add TextureAtlasDesc
change TextureAtlasLoader to a libgdx asset loader class
add AssetManager instance to GameApp. initialize with our custom loaders
TextureAtlasDesc can really just be a static class like it was before..
convenience methods for loading a bit easily
all custom asset loading to be under a common sub-package
'loaders' is probably a better name for it
remove support for loading via json file without an AssetManager
make TextureAtlasJsonLoader private

should really be using libgdx's AssetManager for this kind of thing
rename this subpackage again for fun and profit
add AssetLoadingException
use AssetLoadingException for throwing exceptions during asset loading

duh
dont do this TextureAtlasAnimator in the TextureAtlas loading params

we'll add another way to do this shortly. i forsee too many weird
issues doing it this way (mostly surrounding inconsistently
registering atlases with the animator object)
add method to TextureAtlasAnimator for adding all TextureAtlas objects currently loaded in an AssetManager
add TextureAtlasAnimator.reset method
add MaterialTileMapping
take out the TextureAtlas dependency. we'll reverse it (optional dependency)