[libbluez-qt] Rewrite BluetoothDevice.

- Fixed to wait for the result of GetProperties() before returning
  property values. The ready() signal is emitted when properties
  are available.
- Made alias writable
- Added various missing property NOTIFY signals
- Added audioConnectionState and classOfDevice properties
- Fixed to not crash if connectAudio() is called and the device does
  not support A2DP or HSP
- Removed pairing functionality (should be done via the
  org.bluez.Adapter interface instead)
- Removed input and serial connection functionality