Refactored TTexture to allow encoding sprite(s) at an arbitrary location within
a (possibly shared) physical texture.
The original variant only allowed encoding a sprite at the bottomleft of a
larger physical texture to use NPOT sprites on POT only supporting systems.
a6924450e694
added rq-sky to themes so it can set sky color for low quality. also added tint of sky on sudden death. underwater theme is an example of this
