Close scan screen when pairing and remove device when unpairing.

Close the scan screen after successful pairing, and remove a
device from the list of paired devices after unpairing.

As part of the fix, BluetoothSettings was refactored into a parent
class, DeviceListPreferenceFragment, and three subclasses for each
variant type: BluetoothSettings, BluetoothFindNearby, and
DevicePickerFragment, replacing the checks against mScreenType with
custom logic in the child classes.

Bug: 3325848
Change-Id: If64fddc3ba5b4f1136451491c7d5a1139b696e47

src/com/android/settings/Settings.java

@@ -124,7 +124,7 @@ public class Settings extends PreferenceActivity {
 
     /**
      * Switch to parent fragment and store the grand parent's info
-     * @param class name of the activity wrapper for the parent fragment.
+     * @param className name of the activity wrapper for the parent fragment.
      */
     private void switchToParent(String className) {
         final ComponentName cn = new ComponentName(this, className);