Bluetooth Backend

[Philip]

Hello!

I've made some progress towards bluetooth connections (I'm just focusing on 
the Android side for now). You can see my code at 
https://github.com/Cliabhach/kdeconnect-android/tree/feature/bluetooth . I 
haven't had as much time as I had hoped to work on this. With luck I'll make 
some more progress this weekend.

I do want to get input on some things, if I can:
- What terminology do I use to distinguish the bluetooth pairing process from 
the KDE Connect one?
- Would it matter greatly if I sent the serialized NetworkPackage and its 
Payload in one stream?
- What UUID should we use for KDE Connect's bluetooth service?
- Does my code look sane?

I've not quite managed to get two devices to introduce themselves. They'll 
connect, then timeout while waiting for input/output.

~Philip Cohn-Cort