Initial rtt support
Fix text render
Broken but functional main menu
Added missing overrides for D3D9 renderer
Removed invalid / unneeded include
Fixed z-fighting in the intro
Clear fbo
Fix main menu background
Merge remote-tracking branch 'origin/gamma' into rtt-experiment

Conflicts:
	src/core/ArxGame.cpp
	src/gui/MenuPublic.cpp
	src/window/D3D9Window.cpp
	src/window/D3D9Window.h
Basic shader gamma correction