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)


Origin commit data
------------------
Commit: e490f84ea8
Author: Stefan Seyfried <seife@tuxbox-git.slipkontur.de>
Date: 2017-02-05 (Sun, 05 Feb 2017)

src/gui/widget/keychooser.h

@@ -35,14 +35,13 @@
 
 #include <string>
 
-#include <driver/framebuffer.h>
 #include <driver/fontrenderer.h>
 #include <driver/rcinput.h>
 #include <system/localize.h>
 
 #include "menue.h"
 
-
+class CFrameBuffer;
 class CKeyChooserItem;
 class CKeyChooserItemNoKey;
 class CKeyChooser : public CMenuWidget