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