Universal Image Loader update to use the cache better

Universal Image Loader (UIL) was added to F-Droid a long time ago, and it now provides a lot more features we need. It also has some things that make our customizations obsolete. One key feature this adds is that UIL is paused when the user is scrolling. That should improve UI performance, especially on more limited devices.

This also should make it easier to experiment with more UIL tweaking, like !653 (closed). It does conflict with !653 (closed) though, since it touches the same code.