Add 'auto' mode for eTRV & Thermostat

[Achronite]

After purchasing a Drayton Wiser system, this and (possibly) other, heating systems support three mode of operation:

1. 'Auto'
2. 'Heat'
3. 'Off'

This was discussed with @genestealer before in #47. But after thinking about this more I would like to modify the modes of the eTRV and Thermostat to work in the same way as the wiser system, specifically:

Auto = VALVE_STATE 2 (auto)
Heat = VALVE_STATE 0 (open)
Off = VALVE_STATE 1 (off)

[genestealer]

@Achronite I'm happy to test this but one thing to bear in mind is there may be some confusion if the thermostat set to heat mode and then keeps with the option of setting a temperature. As the set temperature will have no influence when the valve is fully open.

There's also the factor to bear in mind that we're unable to queue commands, unlike zigbee systems, so switching the modes back and forth and setting the temperature need to be two separate actions spaced appropriately apart to allow them both to be picked up by the valve.

[Achronite]

bear in mind is there may be some confusion if the thermostat set to heat mode and then keeps with the option of setting a temperature. As the set temperature will have no influence when the valve is fully open.

Please see #91, I'm planning to release the two together.

So normally, leave it on 'auto' and change the temperatures for the room; letting the boiler state determine if it 'heating' or 'off''.

Do you have a smart boiler system, that can be linked in this way?

[genestealer]

To confirm (to avoid misunderstanding, sorry if this is not what you mean): I would advise against setting the eTRV to off/closed regardless of climate state of the heating source (I.E. Heating/Boiler/heat-pump etc), because the eTRV will no longer perform the "calibration" / "excise valve" when in the closed state.

Yes I agree the best option (if I understood correctly) setting the eTRV to auto at all times and letting the heat-source on/off state determine if it 'heating' or 'off''.

I will add more detail to #91 about the eTRV to heat-source linking/follow.

[genestealer]

I think this can be closed as no longer required, as this is addressed indireclty by #98