Prevent wifi icon from disappearing

Made changes to WifiSettings that customizes
the preference icon so that the icon is never
null. This greatly reduces jittering.

Bug: 29979747
Change-Id: I3d2767310513389c09a37e34674a304278f4d0de

res/drawable/ic_wifi_signal_0.xml

@@ -0,0 +1,26 @@
+<?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.
+-->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+  android:width="26dp"
+  android:height="24dp"
+  android:viewportWidth="26"
+  android:viewportHeight="24">
+  <path
+    android:fillAlpha="0.3"
+    android:fillColor="?attr/wifi_signal_color"
+    android:pathData="M13.0,22.0L25.6,6.5C25.1,6.1 20.3,2.1 13.0,2.1S0.9,6.1 0.4,6.5L13.0,22.0L13.0,22.0L13.0,22.0L13.0,22.0L13.0,22.0z"/>
+</vector>