Return Reference from createBitmapFrom(Local)Texture

This makes clear that pointer ownership is transfered to the caller.
See see GotW 90 solution 2 at
http://herbsutter.com/2013/05/30/gotw-90-solution-factories/
Use auto, now that a reference is returned
Read-only access to Reference in getLocalBitmap
Require Reference to Bitmaps in createMeshFromBitmaps

PixelAccessors are created for the Bitmaps using References, too.