replace fontrenderer.h include with forward declaration

in order to flatten the build dependency tree further, include
fontrenderer.h directly where needed, in header files a forward
declaration is enough

src/gui/moviebrowser/mb.cpp

@@ -74,6 +74,7 @@
 #include <system/ytcache.h>
 #include <zapit/debug.h>
 #include <driver/moviecut.h>
+#include <driver/fontrenderer.h>
 
 #include <timerdclient/timerdclient.h>
 #include <system/hddstat.h>