autodiscovery.py: Change thermostat mode from 'heat' to 'auto'

[Cymaphore]

Change to cause the Thermostat to report mode 'auto'. This is done by setting auto as the only available mode, using the state topic as mode state topic and providing a static mode state topic enforcing state auto.

This way the thermostat is properly visualised and not assumed to be always off.

[edit] Additional commit added by push: Configurable polling, schedule for specified minute of every hour