[warmup] Fixes & Enhancements

[jamesmelville]

Enhancements to the Warmup binding:

1. Documentation updates to reflect that it supports a range of devices
2. Fix to targetTemperature channel - this was broken by a UoM change to the multiply function
3. Add a fixedTemperature channel - sets a fixed mode where the setpoint does not vary on a schedule
4. Add an energyToday channel - reports cumulative energy usage
5. Make runMode writeable to return the mode to a schedule
6. Add thing action for dynamic overrides

[jamesmelville]

Thank you for all the feedback @clinique - I learnt a lot from that. I think I've applied all your suggestions, and also did a bit of further tidying with the RoomHandler class - I hope it all looks better.

[lsiepel]

Gentle ping @jamesmelville

[jamesmelville]

Sorry @lsiepel - this fell off my radar, thank you for all the feedback, I do intend to get back to this in the near future to get it finished!