JSON as payload in MQTT

Better exception logging for modbus

Basic implementation of aggregated values

Modbus: add datatype int32 + tests

Dirty fix: caculcate powerTotal for my new meter

Fix logging

Lot of connection management rework. Added support for reading SML from

serial

VEBus grid meter: expire values not updated for a certain amount of

time.

This is important. When the grid meter fails to read, VEBus must switch
to "no data", so that the battery is not charged/uncharged anymore

Victron DBus improvments + cleanup

Fix NPE in MQTTOutput