MQTT: WIP, re-organized disconnection handling, now keep track of connection status and reconnect accordingly.

This fixes bug with non-reconnecting to broker when having no published variables.

<?xml version='1.0' encoding='utf-8'?>
<BeremizRoot URI_location="ERPC://localhost:61131">
  <TargetType/>
  <Libraries Enable_Native_Library="true" Enable_Python_Library="false"/>
</BeremizRoot>