Faster Shadows, better Gamma Correction, fixes

- Implemented Stencil Masking to speed up PCF Sun Shadows (
http://www2.disney.co.uk/cms_res/blackrockstudio/pdf/Rendering_Techniques_in_SplitSecond.pdf
)
- Added dynamic branching for the Sun Shadows
- Slightly better Gamma Correction
- Fixed Sky Bug when using Sky Entities/Domes instead of Skyboxes
- some small fixes and tweaks here and there