[FEATURE] devicesToPublishAsAccessoriesSwitch allow single switch to control devices with only PowerOn/PowerOff commands
**Is your feature request related to a problem? Please describe.**
Currently for devices with only PowerOn/PowerOff commands, the option devicesToPublishAsAccessoriesSwitch will create two separate switches, one for PowerOn and the other for PowerOff. This can break scenes relying on the status of switches. For example a scene used to turn off all lights need to set the PowerOff switch On, but after timeout the PowerOff switch is off again and the scene is deactivated.

**Describe the solution you'd like**
Optionally allow a single switch to control both PowerOn and PowerOff commands. When the switch is turned on, it sends PowerOn, and when the switch is turned off it sends PowerOff.

**Describe alternatives you've considered**
No real alternatives that I can think of

**Additional context**
The option allowing a single switch to send PowerOn/PowerOff commands can potentially break the synchronisation of device status. A few considerations:
1) Is it possible to sync device status by Harmony API so if the device is turned on by Harmony remote, the on status can be sync to HomeKit? This would be the best option if possible.
2) The sync will not be a problem if we only use HomeKit Harmony plugin to control the device. If we can persist the On/Off status it will even survive the restart 
3) If the device is out of sync it's not the end of the world - when the switch is toggled it just does nothing but to sync the state. For example when the device is On but HomeKit thinks it's Off, when I toggle in HomeKit it sends PowerOn and set the state On. Now the state is in sync.