[feat] Dryer only mode

[tomtom13]

Hi, I think (again stupid me for thinking) that it might be useful for people to use this thermostat in DRYer mode only. Reason is that is might be dumb to switch on dehumidifier while window OR door is open, while is perfectly OK to switch on heating / cooling with room door open. Of-course this functionality might be already there, however I don't see support for "dry" mode only. Also there is a bug in description: The dryer will turn on when the humidity is above the target humidity and the [moist_tolerance](https://github.com/swingerman/ha-dual-smart-thermostat/issues/new#moist_tolerance) is not reached. If the humidity is above the target humidity and the [moist_tolerance](https://github.com/swingerman/ha-dual-smart-thermostat/issues/new#moist_tolerance) is reached the dryer will stop. where second use of "moist_tolerance" is meant to be "dry_tolerance". Yeah, I'm one of those dummies that read docs :)