Include wifi certificates in settings

Deleting wifi certificates isn't supported yet since cascading the
removal back into wifi configs will need some easy way of enumerating
wifi configs first.

Bug: 29208062
Change-Id: I2d9d1ea7e0974701009bfa6ea162b8bc80806639

res/layout/user_credential_preference.xml

@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2016 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="fill_parent"
+    android:layout_height="wrap_content"
+    android:orientation="horizontal"
+    android:gravity="center_vertical"
+    android:background="?android:attr/selectableItemBackground"
+    android:paddingTop="15dip"
+    android:paddingBottom="15dip">
+
+    <ImageView
+        android:id="@+id/icon"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:paddingEnd="?android:attr/listPreferredItemPaddingStart"
+        android:src="@android:drawable/ic_lock_lock"
+        android:tint="?android:attr/colorAccent"/>
+
+    <include layout="@layout/user_credential"/>
+</LinearLayout>