Enable reverse tethering in BT settings screen.

- Enable support for reverse tethering in BT settings.
- Add string resource for "Auto connect" preference.
- Remove unused imports and other minor cleanups.
- Add isConnectable() and isAutoConnectable() methods to Profile
  enum type and remove isConnectableProfile() method.

Change-Id: Ie606db04028a8278e98231f0671a388671f2f067

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

@@ -27,7 +27,6 @@ import android.content.IntentFilter;
 import android.preference.Preference;
 import android.preference.CheckBoxPreference;
 import android.provider.Settings;
-import android.text.TextUtils;
 import android.widget.Toast;
 
 /**