* introduced G2Core::RenderLayer -> an enum having 30 render layers which can be bit combined
 * added RenderLayer::RenderLayerMask to G2::RenderComponent
 * added new Pass Settings block variables RenderLayerIncludes and RenderLayerExcludes defining lists of G2Core::RenderLayer to include/exclude during pass rendering -> also added documentation
 * implemented RenderLayer supported rendering for passes
 * extended interface of intersect method of G2::RenderSystem to get a RenderLayerMask as argument to skip certain G2::RenderComponents entirely if wanted