Move Java Blimp shell code to app subpackage

blimp/client/app/android/java/src/org/chromium/blimp/app/settings/Preferences.java

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-package org.chromium.blimp.settings;
+package org.chromium.blimp.app.settings;
 
 import android.app.Activity;
 import android.os.Bundle;
 
 /**
  * An activity to display the settings and version info.
  */
 public class Preferences extends Activity {
     private static final String TAG = "Preferences";
 
     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         getFragmentManager()
                 .beginTransaction()
                 .replace(android.R.id.content, new AboutBlimpPreferences())
                 .commit();
     }
 }