add support for pvoutput extended values and text message

[nmors]

This PR adds support for PVOutput's extended values and text message fields.

This feature requires donation of $15 per year to PVOutput.org,

Example of mapping additional inverter outputs to these values is in this PR -> https://github.com/meltaxa/solariot/pull/76

Tested & working (You can see an example of this in action here )