- add GLSL postprocessing shader to world view and have it replicate the old gamma ramp
- clear framebuffer between frames to fix visual bugs outside map
- remove old gamma ramp code (was disabled) and remove gamma adjustments to hud elements as they're now unaffected by the shader
- additional visual preset config updates
* Removed superfluous configurations
* Removed superfluous include directories and hard-coded library locations
* There are now only 3 configurations: Debug, Playtest and Release
* Debug and Playtest have the PLAYTEST and BALANCE_ENABLED preprocessor commands, while release doesn't
* Release has maximum optimisations enabled. Debug has none, and playtest has minimal
* Removed hard-coded output directories based on half-life installations, dlls are output in the solution folder (and user can customise as they see fit)
* All projects for all configurations compile without warnings or errors
