this change adds support for a second Victron MPPT charge controller
using a second serial connection.
* Add device configuration for a second victron mppt
* Update VedirectView for second victron mppt
* Update MqttHandleVedirect for second victron mppt
* Update MqttHandleVedirectHass for second victron mppt
* Handle nonexisting victron controllers with optionals
* Add bool-function to Battery and inherited classes, if uart port 2 is
being used
* Introduced a serial port manager. In order to prevent the battery and
the Victron MPPT to use the same hw serial ports, this class keeps
track of the used ports and their owners.
