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/system/httptool.cpp

@@ -18,6 +18,7 @@
 	Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA
 */
 
+#include <config.h>
 #include <cstring>
 #include <system/httptool.h>