Add Settings support for Bluetooth Multi-A2DP and Multi-HFP

When there are multiple connected A2DP/HFP devices, if a connected
device's name is clicked on, that device will be chosen as
Active - i.e., it will be the device chosen for audio out / phone call.

Test: Manual: multiple connected A2DP devices, and selecting each as
      the Active Device.
Bug: 64767509

Change-Id: Iee76286110ed87703d6a968f50273c22cd7c7086

src/com/android/settings/bluetooth/DeviceListPreferenceFragment.java

@@ -277,6 +277,9 @@ public abstract class DeviceListPreferenceFragment extends
 
     public void onConnectionStateChanged(CachedBluetoothDevice cachedDevice, int state) { }
 
+    @Override
+    public void onActiveDeviceChanged(CachedBluetoothDevice activeDevice, int bluetoothProfile) { }
+
     /**
      * Return the key of the {@link PreferenceGroup} that contains the bluetooth devices
      */