SpriteAsset not setting width/height properly

[Bjeaurn]

Width and height are being set by the Asset class, which takes it from the actual image. But in the case of a sprite, we don't want the full width/height of the image; cause we're only using a small part of the actual image for our sprite.

The sprite width/height should be set and equal to sizeX and sizeY.

Maybe refactor sizeX and sizeY to actually reflect width/height, I'm not sure if they have a separate function within the class.