Add L2TP secret, L2TP/IPSec PSK support. Fix screen orientation.

* Changes
  + Add L2tpActor, L2tpEditor, L2tpIpsecPskActor.
  + Make L2tpIpsecEditor extend L2tpEditor.
  + Revise the code for saving username. Make
    VpnSettings.saveProfileToStorage() static.
  + Fix support for screen orientation change in both VpnSettings and
    VpnEditor.

  Patch Set 2:
  + Remove Util.isNullOrEmpty(). Use TextUtils.isEmpty() instead.
  + Remove unused imports. Wrap lines longer than 80 chars.

  Patch Set 3:
  + Fix all the strings according to UI feedback.
  + Remove all the added actor subclasses and move password to editor.
  + Remove VPN entry in Security & location.

  Patch Set 4:
  + Misc string fixes.

  Patch Set 5:
  + Add strings for credential storage settings.
  + Changed the error dialog icon.
  + Fix "Remember me" indentation in connect dialog.

  Patch Set 6:
  + resolve res/values/strings.xml

src/com/android/settings/SecuritySettings.java

@@ -28,7 +28,6 @@ import android.content.Intent;
 import android.content.pm.PackageManager.NameNotFoundException;
 import android.database.Cursor;
 import android.location.LocationManager;
-import android.net.vpn.VpnManager;
 import android.os.Bundle;
 import android.preference.CheckBoxPreference;
 import android.preference.Preference;
@@ -198,17 +197,6 @@ public class SecuritySettings extends PreferenceActivity implements
         showPassword.setPersistent(false);
         passwordsCat.addPreference(showPassword);
         
-        PreferenceScreen vpnPreferences = getPreferenceManager()
-                .createPreferenceScreen(this);
-        vpnPreferences.setTitle(R.string.vpn_settings_title);
-        vpnPreferences.setSummary(R.string.vpn_settings_summary);
-        vpnPreferences.setIntent(new VpnManager(this).createSettingsActivityIntent());
-
-        PreferenceCategory vpnCat = new PreferenceCategory(this);
-        vpnCat.setTitle(R.string.vpn_settings_category);
-        root.addPreference(vpnCat);
-        vpnCat.addPreference(vpnPreferences);
-
         return root;
     }