* JK BMS: avoid trailing whitespace in debug output
* JK BMS: publish data points through MQTT
* JK BMS: updateFrom: skip data points with equal value
this changes the interpretation of the timestamp in data containers that
are merely updated from other data containers: this is the oldest
timestamp known where the value was as recorded by the data point in its
respective container.
the data container constructed from an answer will -- naturally -- have
the timetamps of its data points set to the time they were constructed.
* JK BMS: only publish changed values to MQTT broker
all values are still published once every minute if the MQTT retain flag
is NOT set. otherwise, the constant values are only published once on
startup.
