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/upnpbrowser.h

@@ -23,7 +23,6 @@
 #ifndef __upnpplayergui__
 #define __upnpplayergui__
 
-#include <driver/framebuffer.h>
 #include <driver/audiofile.h>
 #include <driver/pictureviewer/pictureviewer.h>
 #include <gui/filebrowser.h>
@@ -58,6 +57,7 @@ struct UPnPEntry
 	int		type;
 };
 
+class CFrameBuffer;
 class CUpnpBrowserGui : public CMenuTarget, public CListHelpers
 {
 	public: