Add Anchor Point to SpriteSheet

I have add the ability for the SpriteSheetLoader and JsonLoader to check for a .AnchorPoint field. 
Using a Pixi Style Anchor Point this add the point to the Texture that is being loaded.
when the sprite is crated or texture updated it automatically changes the anchor point of the sprite to that of the texture.

I add this function for sprite texture of changing shape and size to get a common point to link up with even if that point change locations with in the sprites image.