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.cpp

@@ -256,7 +256,7 @@ void UITask::buttonHandler() {
           digitalWrite(PIN_STATUS_LED, LOW);
           delay(10);
         #endif
-          _board->powerOff();
+          shutdown();
         }
       }
       btn_state_change_time = millis();
@@ -267,6 +267,29 @@ void UITask::buttonHandler() {
 #endif
 }
 
+/* hardware-agnostic pre-shutdown activity should be done here 
+*/
+void UITask::shutdown(bool restart){
+
+  #ifdef PIN_BUZZER
+  /* note: we have a choice here -
+     we can do a blocking buzzer.loop() with non-deterministic consequences
+     or we can set a flag and delay the shutdown for a couple of seconds
+     while a non-blocking buzzer.loop() plays out in UITask::loop()
+  */
+  buzzer.shutdown();
+  uint32_t buzzer_timer = millis(); // fail-safe shutdown
+  while (buzzer.isPlaying() && (millis() - 2500) < buzzer_timer)
+    buzzer.loop();
+
+  #endif // PIN_BUZZER
+
+  if (restart)
+    _board->reboot();
+  else
+    _board->powerOff();
+}
+
 void UITask::loop() {
   buttonHandler();
   userLedHandler();

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();
 };