Volley images

Add support for using Volley to load remote images instead of UIL

1. Gives us Caching
2. Load images at full resolution, rather than hardcode them. This is done by trying to fetch an image at highest width possible for the particular view. If it 500s, we assume that the image is smaller than the requested width and just request the full size image
3. Created a MediaWikiImageView, to which you can pass a Media object and it will display it. Takes care of sizing, etc. Optionally you can also specify a view to use as the 'loading' view.

TODO:
Loading from content:// URIs still use UIL. Need to write a Volley HTTP Stack that can fake responses for content:// URIs.