Renderers: refactor recomposition methods

Renderers: refactor recomposition methods

- Adds support in GraphicSystem for accepting a LayerList to
  render, instead of only one Layer.  This enables future
  optimizations that change the rendering order.
      eg. - reverse render order to utilize depth test culling
          - draw multiple layers/surfaces at once (multitexturing)

  also includes a 'clear' flag so the background clear can be
  optimized as well.
      eg. - no need to clear obscurred pixels

- Don't reset any damage flags until after rendering has taken
  place.  Detailed damage information could be useful to the
  GraphicSystem when it is rendering.  Wait until after
  recomposition, then clear all flags. Share the routine to
  clear damage flags in the BaseWindowSystem.