Refactoring: RegionAttachment vertices, texture->rendererObject...

- Vertices are no longer stored on RegionAttachment. The vertices are temporary state, not part of RegionAttachment's persistent state like UVs and offset.
- AtlasPage and RegionAttachment "texture" field is renamed to "rendererObject". This is a better name as it may not be a texture.
- AtlasAttachmentLoader uses the AtlasRegion as the rendererObject. This enables a renderer to use region information if needed. The page rendererObject is still available.
- Better "enum" look up for AS3.
- Unity4 example doesn't use a compressed material.
Refactoring: changed references to "bind pose" to "setup pose".

This better matches "setup mode" in the editor and we can be consistent in code and docs from now on.
Better JSON code.
Merge branch 'master' into monogame