Update: Add support for the "off" thermostat mode and the SwitchLevel capability
I added support for the "off" thermostat mode. When in the "off" mode, there will be no thermostat control of linked fans; control will be fully manual.
This also adds support fot the SwitchLevel capability. The setLevel command can be used to control the fan speed just like setSpeed. The range is split into a number of equal-sized ranges that each set the fan to a given speed. For example, for a 3-speed fan, level 1-33 will set the fan to low, 34-66 to medium and 67-99 high. When the thermostat sets the fan speed it will set the level to the bottom of the corresponding range.