Add menu for changing sort column and sort direction

This is essentially a copy of the code in Kleopatra. Upstreaming the
code to libkleo makes it possible to add this menu also to the other
TreeView-based tables in Kleopatra.

(cherry picked from commit 918050cb3064d2a3a3a052c87d135cff4b7d181c)

• GnuPG-bug-id: T6568