Maxcul binding initial implementation (#1085)

This is an initial pull request for the Max!CUL binding implementation as per #1085.

Currently it has the ability (tested) to pair a radiator thermostat and wall thermostat unit. 

Wall thermostat units have bi-directional communication (i.e. desired temperature can be set from OpenHAB and openhab will update the unit and vice versa).

For radiator thermostat units you can only set the desired temperature from openhab, not from thermostat to openhab. Hopefully this will be done next as well as starting a wiki page :)
afaik the "credit" is a feature that applies to all implementations working on the same frequency. So wouldn't this functionality better fit in the io.transport.cul bundle?