Misc tweak on wifi hotspot setting page

- Make hotspot password show in plain text
- Make main control into a master switch style

Change-Id: I8fdb293a617787f256fb663708cfc0e454f548d2
Fixes: 63865785
Test: robotests

src/com/android/settings/wifi/tether/NoOpOnStartTetheringCallback.java

@@ -18,6 +18,10 @@ package com.android.settings.wifi.tether;
 
 import android.net.ConnectivityManager;
 
-class NoOpOnStartTetheringCallback extends ConnectivityManager.OnStartTetheringCallback {
+class NoOpOnStartTetheringCallback {
 
+    public static ConnectivityManager.OnStartTetheringCallback newInstance() {
+        return new ConnectivityManager.OnStartTetheringCallback() {
+        };
+    }
 }