Reduces stutter and freezes when playing.
* Maintains double SM and SM Color textures
* Light frustum update triggers incremental generation of shadow map into secondary 'future' textures.
* Every incremental update renders a portion of the shadow draw list (split equally).
* After defined number of frames (currently, 4), 'future' and 'current' textures are swapped, and DirectionalLight 'commits' the new frustum to use when rendering shadows on screen.
Co-authored-by: sfan5 <sfan5@live.de>
