DeviceItem: Show adapter name when one device is available in multiple adapters
Reduce sections to only Connected and Available

Bluez is automatically removing unused devices found during
device discovery.
Pairing with or connecting to the device saves the device
permanently. Some other devices (eg. PS3 controller) won't also
be ever automatically removed.

It does not makes sense to favorize those devices in device list in
Available devices category over Paired devices.