vsync setting for OpenGL

probably won't override driver settings, of course but I had to try

Conflicts:
	src/Engine/Options.cpp
Merge branch 'opengl' of github.com:hmaon/OpenXcom into opengl

Conflicts:
	src/Engine/Options.cpp
Merge branch 'opengl' of github.com:hmaon/OpenXcom

Conflicts:
	src/Engine/Game.cpp
	src/Engine/OpenGL.cpp
	src/Engine/OpenGL.h
	src/Engine/Options.cpp
	src/Engine/Screen.cpp
	src/Engine/Screen.h
Merge branch 'master' of github.com:hmaon/OpenXcom

Conflicts:
	src/Engine/Options.cpp
	src/Engine/Screen.h

what even happened