InstalledPage: sort descending unless sorting by name

When sorting the Installed page do it in descending order unless it's the package name.

This the most sense when sorting by size, as the user is probably looking to free some space, but I think it works well for rating and release date too.

Maybe there should be a button to flip the sorting, but since this is my first contribution I'm keeping it tiny. I'm open to look at it though.