Make column visibility and sort order keyboard-accessible in KeyTreeView

Add the column menus to the default KeyTreeView context menu. This makes
it possible to change the visible columns and the sort order with the
keyboard in the edit group dialog, the group details dialog, and the
imported certificates dialog.

(cherry picked from commit c770d6a4e14269072600b76b135669c8b85a5846)

• GnuPG-bug-id: T6568