Refactor to a data model

Image information and repo information are now both stored somewhere
else entirely, so we don't need to keep accessing weird API return
values to sort things out. fetchImageInfo now uses those classes to
an extent, and we now cache thumbnail URLs for different sizes.

Change-Id: Ife8293c86683ea914b1a5a60000584b501d92e55
Merge "Refactor to a data model"