Workaround : Introduce the viewport notion. SDL_RenderSetClipRect seems to be relative to the point 0,0 of the window instead of the viewport. It fixes fullscreen and resized windows.

Conflicts:

	include/Common.h
	include/lowlevel/VideoManager.h
	src/lowlevel/VideoManager.cpp
Fix the viewport workaround
Update the viewport when changing the video mode
Fix compilation error due to bad merge.