Clean up PV Voltage, Current and Power paths on D-Bus

[mpvader]

This change was put in motion due to some differences between how vedirect-interface puts the tracker info on the D-Bus, and how vecan-dbus does it; also vrmlogger didn't transmit the Watts per tracker. Instead it transmitted Volts & Amps; which seems ok at first, but when you think about it its wrong: the main number here are the watts; and when a small current is rounded to 0, then suddenly Watts is reported as 0 while its not 0.

Also, after taking a closer look, and knowing that signal-changes on D-Bus heavily affect cpu load and thus scalability wrt max number of devices, we decided to take the /Pv/I away. UIs can self-calculate that, by simply dividing the power by the voltage.

The vrmlogger issue, now solved, was causing issues on the VRM Dashboard at the moment, where Teun is trying to get all trackers visual in the detailed box.

Todo list:

• (mva) update our dbus wiki page.
• (ibu) vrmlogger needs changing to report Voltage & Power for those two trackers (backport candidate for v2.73)
• (tve) remove the paths for PV current: /Pv/x/I, as well as the far longer existing /Pv/I.
• (mbo) check that dbus-vecan is in sync, also for the Inverter RS (which is now no longer supported by vedirect-interface!)
• (mva) arrange the VRM Advanced graphs to calculate current rather than take it from the database.
• (tve) fix up the relevant pages in the gui/qml.
• (dfa) update node-red nodes for this
• (ibu) remove /Pv/I from vrmlogger
• (ibu) check if we need to do something with modbus-tcp; or some other consumer that I'm now forgetting

System to test this on:
https://vrm.victronenergy.com/installation/55013/overview

vedirect-interface:

vecan-dbus:

vrmlogger:

[mpvader]

All done, closing.