fix for potential access to no longer existing Message instances in DataHandler, validate MQTT topic during argument parsing, extended DataHandler registration to allow registering multiple instances at once, only create MqttHandler if active

src/lib/ebus/message.cpp

@@ -2559,8 +2559,10 @@ void MessageMap::invalidateCache(Message* message) {
 
 void MessageMap::addPollMessage(bool toFront, Message* message) {
   if (message != NULL && message->getPollPriority() > 0) {
+    lock();
     message->m_lastPollTime = toFront ? 0 : m_pollMessages.size();
     m_pollMessages.push(message);
+    unlock();
   }
 }