Properly handle renames.

Renames with no additional changes have no patch attached, so we
shouldn't make those clickable. As a non-clickable entry under 'Files
Changed' would be a little confusing, introduce a separate header for
renamed files.
Restore possibility to view changed image files.
Refactor issue list activity.

In order to make it consistent to the pull request activity, have
open/closed tabs instead of having 3 tabs that present the same data in
different sort orders. Make the sort order selectable by a menu instead.