Add fan_mode property to humidifier component

Hello,
would be great to have the option to set the fan_mode property (fan speed) of an humidifier/dehumi, as it already exists for the Climate component. So that property should be added to the component homeassistant/components/humidifier/__init__.py, and it can be easily copy-pasted from the Climate component (homeassistant/components/climate/__init__.py).

Thank you so much