fixed maximum size of QuadBatch

That old value has been in there since the beginning; either I had it wrong back then, or the stage3D specification changed. ;-) Thanks to shin10 for making me aware of this!
added new 'TextureOptions' class, used by 'Texture.fromData' and 'AssetManager.enqueueWithName'

In the Texture class, this makes the huge number of parameters to the "from..."-methods easier to handle; in the AssetManager, this allows to supply custom options for each added texture.