Remove BluetoothDiscoveryModel inconsistency

The BluetoothDeviceDiscoveryModel has some inconsistencies which need to be checked:

• newServiceDiscovered()
  • parameter not documented
• newDeviceDiscovered()
  • should signal have a parameter?
  • how to retrieve the found devices (if not via signal)
  • the overloading of data model content depending on the search may be confusing

These issues require potential API changes and must be addressed before API freeze.