Per vpn setting change in VPN list

- Show admin support details when user taps on a cell and user restriction is on
- Show always-on-vpn active status in preference summary
- User can still open non-configurable per-VPN info page even when user restriction is applied
- Rename ConfigPreference to LegacyVpnPreference
- Move summary String handling into ManageablePreference
- ManageablePreference inherits GearPreference to reuse the code
- Don't show disconnect dialog when always-on is enabled

BUG=26950700

Change-Id: I37b087879cf3b674df528e7787d7bb1eead3310f

res/layout/preference_vpn.xml

@@ -1,39 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!-- Copyright (C) 2015 The Android Open Source Project
-
-     Licensed under the Apache License, Version 2.0 (the "License");
-     you may not use this file except in compliance with the License.
-     You may obtain a copy of the License at
-
-          http://www.apache.org/licenses/LICENSE-2.0
-
-     Unless required by applicable law or agreed to in writing, software
-     distributed under the License is distributed on an "AS IS" BASIS,
-     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-     See the License for the specific language governing permissions and
-     limitations under the License.
--->
-
-<LinearLayout
-        xmlns:android="http://schemas.android.com/apk/res/android"
-        android:layout_width="wrap_content"
-        android:layout_height="match_parent"
-        android:orientation="horizontal">
-    <View
-        android:id="@+id/divider_manage"
-        android:layout_width="2dip"
-        android:layout_height="match_parent"
-        android:layout_marginTop="5dip"
-        android:layout_marginBottom="5dip"
-        android:background="@android:drawable/divider_horizontal_dark" />
-    <ImageView
-        android:id="@+id/manage"
-        android:layout_width="wrap_content"
-        android:layout_height="fill_parent"
-        android:paddingStart="16dip"
-        android:paddingEnd="16dip"
-        android:src="@drawable/ic_sysbar_quicksettings"
-        android:contentDescription="@string/settings_label"
-        android:layout_gravity="center"
-        android:background="?android:attr/selectableItemBackground" />
-</LinearLayout>