playback menu entry

UIThread.cpp

@@ -200,6 +200,16 @@ static void handleInput() {
               }
               
               switch(menuItems[menuSelection].id) {
+              case MENU_ID_PLAYBACK:
+                isPlaying = !isPlaying;
+                if (isPlaying) {
+                  playbackStep = 0;
+                  clockCount = 0;
+                  lastClockTime = micros();
+                } else {
+                  queuedTheme = -1;
+                }
+                break;
               case MENU_ID_MELODY:
                 midi.lock();
                 melodySeeds[randomizeTrack] = random(10000);