when performing a test request using the web UI, we need to init() the
respective power meter, but we do not want to start the polling task.
hence we move initialization of the polling task to the poll() function.
it will return if the task is setup already, otherwise setup the task.
implement a function which allows to reset the SML decoder. this new
function is used after a datagram ends. for the SML HTTP power meter
this is simple: after all bytes from the request's answer have been
decoded, we reset the decoder. for the SML serial power meter, we
perform the reset after a datagram ended based on timing (no new bytes
have been received for a specific amount of time).
* when printing a message, tell the name of the derived class.
* print total power only when state SML_FINAL reached.
* tell if a checksum verification error occurred.
this new class handles SML data. it uses the SML lib to decode values
and manages those. this de-duplicates code as the class is applicable
to all power meters that collect SML data.
"powertotal" is always published and it is published by the base class
directly. other values are still published by the derived classes, but
use a base class method, which takes care that a common base topic is
used in particular.
it is important to separate the capabilities of each power meter
provider into their own class/source file, as the providers work
fundamentally different and their implementations must not be
intermangled, which made maintenance and improvements a nightmare
in the past.
