Thermostats: more improvements
All changes:
- Anna + Elga: hide cooling_enable switch, (hardware-)switch is on Elga, not in Plugwise App
- Adam: improve collecting regulation_mode-related data. Fix for #240
- Anna: remove device availability, fix for home-assistant/core#81716
- Anna + OnOff device: fix incorrect heating-state, fix for home-assistant/core#81839
- Improve handling of xml-data missing, raise exception with warning. Solution for home-assistant/core#81672
- Improve handling of empty schedule, fix for #241