some cleanup

[Beeblerox]

i've added mesh and skinned mesh support for SkeletonSprite as well

[bendmorris]

Thanks. Manually merged to resolve a conflict, with two changes:

• In JsonUtils:34 and JsonUtils:40, readInt and readFloat need to be casts. parseInt and parseFloat don't work because the values aren't strings.
• I like the newlines at the ends of my files. http://stackoverflow.com/questions/729692/why-should-files-end-with-a-newline

[Beeblerox]

thanks for merging