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/components/cc_frm_clock.cpp

@@ -36,6 +36,7 @@
 #include <ctype.h>
 #include <system/helpers.h>
 #include <system/debug.h>
+#include <driver/fontrenderer.h>
 
 using namespace std;