trayicon_notification_on_events and do what's expected

about why we do that. Fixes #2636.

More logical meaning of first message for a single message (if no single already in queue for this jid)
Fixed possible bad value of first for pm
Slaped bad bad comments

When some event for a jid arrive and we want show in roster, always show, even if contact is not in the
roster
Generalize selection of incomming event in the roster
separate add_to_not_in_the_roster() in a func
Deleted a Redraw of parent that seems useless (done in draw_contact())
Fixes #2247.

update contact instance in chat control when a resource comes back online (a new contact instance is created). fixes #2619

don't show contact in roster if account is offline and no pending events and show_offline is False. fixes #2618

again fix Gajim so it runs if NM is not there. Stefan please have a look from time to time in the timeline to see other ppl fixes [f.e. this was done by Yann b4]

(options are in ACE only)

missing logic on prefs window for exo-open stuff. fixes #2606. thanks baze for ur attention to detail

mention the link to use more music track players in the tooltip of set_status_msg_from_current_music_track_checkbutton

some events are not readable. thus unread event does not make sense. Pending Events is what we wanna say