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/infoviewer.cpp

@@ -68,6 +68,7 @@
 #include <driver/display.h>
 #include <driver/volume.h>
 #include <driver/radiotext.h>
+#include <driver/fontrenderer.h>
 
 #include <zapit/satconfig.h>
 #include <zapit/femanager.h>