Load images and send them to ImagesFragment

Doesn't show them yet, but we're getting there...
Figured out easier usage of Volley

No need for utils, can just use a singleton for the entire app
Added image loading

Required adding BitmapLruCache, a very simple Bitmap cache.
Added "infinite" scrolling

It's hardly infinite because Google limits you to 64 results on
their deprecated API.  :/
Handle rate limit encounters with Google API

If we hit the rate limit, then we wait a given amount of time and then
try again.
Handle configuration changes in app

E.g., rotating the app will still have it work
Made GridView actually look alright
Made items non-clickable
Made SearchView behavior more reasonable

- Collapses automatically when you start a new image search

- Opens with the current query displayed
Handle all error cases with a single message

This includes the "no results" error case; while I could make a
separate code path for it, I don't think it's necessary for a sample
application.