replace framebuffer.h include with forward declaration

instead of including framebuffer.h almost everywhere, replace it with
class CFrameBuffer forward declarations and/or generic system includes.
Add a hack to define fb_pixel_t to config.h (one reason for
framebuffer.h includes was the fb_pixel_t define)

src/gui/videosettings.h

@@ -31,10 +31,9 @@
 #define __video_setup__
 
 #include <gui/widget/menue.h>
-#include <driver/framebuffer.h>
-
 #include <string>
 
+class CFrameBuffer;
 class CVideoSettings : public CMenuWidget, CChangeObserver
 {
 	private: