[WifiSetup] Add + icon to Add another network

Add the + icon to "Add another network" in Wi-Fi screen in setup
wizard, and make the text black and sentence case.

Bug: 21089864
Change-Id: Iccfc5fc4ff5e50a599f3004a20e5cfa24a13043a

res/drawable/setup_ic_add_another_network.xml

@@ -0,0 +1,30 @@
+<!--
+    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.
+-->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="25.0dp"
+        android:height="32.0dp"
+        android:viewportWidth="38.0"
+        android:viewportHeight="48.0">
+
+    <group android:translateX="5.0" android:translateY="10.0">
+
+        <path
+            android:fillColor="?android:attr/colorControlNormal"
+            android:pathData="M28.0,16.0L16.0,16.0l0.0,12.0l-4.0,0.0L12.0,16.0L0.0,16.0l0.0,-4.0l12.0,0.0L12.0,0.0l4.0,0.0l0.0,12.0l12.0,0.0l0.0,4.0z"/>
+
+    </group>
+
+</vector>