add adapter mac address

[DanielHabenicht]

#432

[DanielHabenicht]

I don't have a mac, nor the time to setup a android development environment. So hopefully thats sufficient for a first implementation?

[qdot]

Blocked on discussion in #432

[gabevenberg]

Even with just the impls currently in place, this would be very helpful for those of us developing linux specific stuff. Id love it if it was possible to expose the entire contents of bluezs AdapterInfo struct.