Add Presence management

This pre-release contains the Presence management.
To activate, edit your Thermostat configuration and add a presence sensor entity id. It's state should be 'On' is someone is present at home or 'Off' else.

When presence turns to off, you have two exclusive choice:

1. set the preset to a defined value ("Away" is certainly the most valuable choice),
2. or add an offset to the current temperature without changing the preset. This offset can be negative of course.

Other content of this pre-release:

1. Add presence management
2. Fix many bugs on states actualisation
3. Add extra attributes with all internal states (useful for tuning the Thermostats attributes)

Enjoy !