- Move Scale9Grid stuff from ImageSprite to SpriteTexture

  Moved all GUI rendering outside of GUIManager and into SpriteManager
   - Make it generic for 2D game purposes

  See SpriteTexture.txt for needed sprite texture updated.

  Check Unity 2D tools for editor functionality: https://www.youtube.com/watch?v=EOX6itCuKOc&feature=youtu.be