Assign OpenPGP is useless
Assign OpenPGP key menu item in roster_contact_context_menu is useless.
Contact may wish not to use a pgp, event if the message is crypted with his public key.
If the assigned PGP is None, the pgp button in chat window is still active - this leads to the illusion that the message can be send ecrypted, although it is send as a plain text.