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/fontrenderer.cpp

@@ -33,6 +33,7 @@
 #include <ft2build.h>
 #include FT_FREETYPE_H
 
+#include <driver/framebuffer.h>
 #include <driver/fontrenderer.h>
 
 #include <system/debug.h>