Usermod enhancements

- added onStateChange() callback
- added examples & comments to usermod_v2_example.h
- PIR sensor cancels countdown on state change

wled00/um_manager.cpp

@@ -40,6 +40,7 @@ bool UsermodManager::onMqttMessage(char* topic, char* payload) {
   return false;
 }
 void UsermodManager::onUpdateBegin(bool init) { for (byte i = 0; i < numMods; i++) ums[i]->onUpdateBegin(init); } // notify usermods that update is to begin
+void UsermodManager::onStateChange(uint8_t mode) { for (byte i = 0; i < numMods; i++) ums[i]->onStateChange(mode); } // notify usermods that WLED state changed
 
 /*
  * Enables usermods to lookup another Usermod.