title: Python-dbus extra param to add_signal_receiver
body: <p>I'd like to pass extra param to add_signal_receiver or get somehow path the signal was received from.
  Now it's defined like that:</p>
  
  <pre><code>bus.add_signal_receiver(handle_signal, 'RemoteDeviceFound', 'org.bluez.Adapter', 'org.bluez', '/org/bluez/hci'+x)
  
  def handle_signal(address, cls, rssi):
      xxxx
  </code></pre>
  
  <p>I wan't to have many signal receivers at the same time and be able to read 'x' inside handle_signal function.</p>