Bka device reference

First steps towards being able to eliminate DeviceReference class.

DeviceReference is effectively struct of dsuid_t and Apartment*. There is no functionality inside the class. It is used as yet one more option how to pass device reference around.

• 50ce4cb7 toJson(Device): avoid getDevice() calls
• 555766fd deviceReference: remove (mostly dead) methods
• 09013fa4 DeviceReference: do not inherit DeviceInterface