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/driver/fb_window.h

@@ -23,8 +23,8 @@
 #define __fb_window_h__
 
 #include <driver/fontrenderer.h>
-#include <driver/framebuffer.h>
 
+class CFrameBuffer;
 class CFBWindow
 {
  public: