enable SkeletonJson to load Objects (not just Strings)

SkeletonJson.readSkeleton() should be able to take Objects also not just Strings. Starlings Assetmanager for example creates an Object already when it loads a json file. So then u have to Stringifiy the result, to put it in readSkeleton(), and this method makes Object again.. quite redundant.

This fix makes it take it as Object also.. skipping another parse process.


Cheers