Support unmodified publish topics through '!'-topic-prefix

• New topic-prefix ! for unmodified publish-topics: By default, munet mqtt prefixes outgoing publish messages with both outDomainPrefix and hostname. In order to support publishing of unprefixed message topics, topics can be prefixed with !. E.g. publishing to topic !test/topic will publish with topic test/topic to the external mqtt server, while publishing to test/topic publishes externally to omu/hostname/test/topic.
• The mqtt component now sends an internal muwerk message to other muwerk processes with topic mqtt/state and message either connected or disconnected.