Add support for Danfoss Eco Thermostat #79

Add support for Danfoss Eco.

The thermostats are used Bluetooth low energy and exposes a few well know services such as the battery service and two custom services.

It is impossible to read or write to any characteristics, until a pin is send to the 10020001-2749-0001-0000-00805F9B042F characteristic. Communication to the two custom services are encrypted with xxtea using a per device key that is exposed via a characteristic (1002000B-2749-0001-0000-00805F9B042F) that is only readable when the paring button on the thermostat is pressed.

Aditonal information

Is the device to "quirky" to consider supporting in this binding or is it something you would be willing to accept a PR for?

Thanks,
/Simon