Resize and keep aspect ration

Only OpenGL mode has been taken into account.
New options:
keepAspectRatio, boolean
cursorInBlackBandsInFullscreen, boolean
cursorInBlackBandsInWindow, boolean
cursorInBlackBandsInBorderlessWindow, boolean
Keep aspect ratio with no OpenGL

Now the "keep aspect ratio" feature functions even when OpenGL is not employed.
Merge branch 'resize-without-deforming' of https://github.com/Juju-Dredd/OpenXcom

Conflicts:
	src/Engine/Options.cpp