Integrate VPN with new keystore and misc fixes.

* Changes
  + Pass intent to keystore when needed and hooks to resume from it.
  + Generate random, unique ID for profile instead of base64 from its
    name.
  + Add VPN to "Wirless controls" description.
  + Add credential storage to "Security & location" description.
  + More hints to set password and unlock dialogs in credential storage
    settings for actions that come from other processes.
  + Sort VPN profiles according to the names.
  + Replace Keystore with CertTool in L2tpIpsecEditor

src/com/android/settings/vpn/L2tpEditor.java

@@ -60,12 +60,6 @@ class L2tpEditor extends VpnProfileEditor {
                 : validate(mSecretString, R.string.vpn_l2tp_secret));
     }
 
-    @Override
-    public void saveSecrets(String originalProfileName) {
-        L2tpProfile profile = (L2tpProfile) getProfile();
-        // TODO: fill up the implementation after keystore is available
-    }
-
     private Preference createSecretPreference(Context c) {
         final L2tpProfile profile = (L2tpProfile) getProfile();
         CheckBoxPreference secret = mSecret = new CheckBoxPreference(c);