Sends broadcast time message over radio.

src/radio.h

@@ -8,6 +8,7 @@ public:
   Radio(Display *d, bool _isMaster):display(d), isMaster(_isMaster) { };
   void begin(void);
   void loop(void);
+  void broadcastClock(int hour, int minute, int second);
 private:
   Display *display;
   bool isMaster;