Send useful logging messages to MQTT

[gskjold]

Send a message to MQTT for certain state changes so that this can be tracked.
This could be:

• When data is substituted because of bad data received (Aidon sending same accumulated values two hours in a row #1119)
• When data stream from the meter has stopped (Feature request: Notification in HA payload when no data from the meter #1120)
• When there are issues fetching prices from server