Updating code sample for "displaying bitmaps efficiently" training class.

Changes:
 -Use updated versions of ImageWorker & ImageCache from I/O 2012 app
 -Use copied DiskLruCache from system (rather than custom)
 -Use copied AsyncTask from system (to keep behavior consistent)
 -Ensure no strict mode violations or lint errors
 -Other misc bug fixes
 -Move single-use static methods in Utils to corresponding class

Change-Id: If21e045db1e1a80391169f3c9c9258d48345ab6b

samples/training/bitmapfun/res/menu/main_menu.xml

@@ -1,4 +1,19 @@
 <?xml version="1.0" encoding="utf-8"?>
+<!--
+  Copyright (C) 2012 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.
+-->
 <menu xmlns:android="http://schemas.android.com/apk/res/android" >
 
     <item