Add energy monitor sensor about pyvera

[pavoni]

@danodemano I'll probably make 'power' in W the main item to display - with energy in kwh as a secondary attribute. Does that make sense to you?

Something like this (excepy in W - kW makes sense for a while house - but probably not for a single device (unless you know better).

[danodemano]

@pavoni - makes sense to me. Watts is most likely the more important one but people will also want to see kwh as well, even for individual devices. That can tell them how much a specific device is costing in electric.

I know when the devices were tied straight to HA through zwave each of their values came across separately (watts, kwh, voltage, amps, etc). Might just make sense to keep it the same.

[pavoni]

I did this the simple way for now (vera sensors are mapped to a single HA device).

Please test it if you can home-assistant/core#7134