Fixes power state (on/off) cache corruption.

[sander1988]

Changes:

• Power on/off as boolean instead of int (the HomeKit specs say it should be a bool).
• Cached value used check changed to 'undefined' checks as they didn't work correctly with bools. "if (!cachedValue)" is also true for a false or 0 value.
• Updated the device value cache only after successful Domoticz calls.
• Always update the characteristic in their setters (even if they seem unchanged). Let HomeBridge handle the check if it should be processed to HomeKit.

[PatchworkBoy]

Done... NPM patched to 2.1.37.