Connect RTTTL shutdown melody to shutdown procedure

Added a new UITask shutdown method to run non-board specific shutdown code.  This avoids having to update all the board files for different hardware.

UITask::shutdown(bool restart = false);

Where the buzzer is available and defined, the RTTTL shutdown melody is played when the button is held down for >5s.

examples/companion_radio/UITask.h

@@ -39,7 +39,6 @@ class UITask {
   void buttonHandler();
   void userLedHandler();
   void renderBatteryIndicator(uint16_t batteryMilliVolts);
-
  
 public:
 
@@ -55,5 +54,6 @@ public:
   void msgRead(int msgcount);
   void newMsg(uint8_t path_len, const char* from_name, const char* text, int msgcount);
   void soundBuzzer(UIEventType bet = UIEventType::none);
+  void shutdown(bool restart = false);
   void loop();
 };