This was somehow lost once we implemented random resource strings
Although its good that initally a random resource is chosen, it
still should persist across sessions.

This helps to kill zombie client connections on the server because
most servers kill the old session once a new with the same resource
connects

Also dont notify the user about resource conflicts if no custom
resource is set. We should not expect users to know about resources
and what they are used for as long as possible.

Add MAM for MUCs

See merge request gajim/gajim!152

A stanza-id is only unique within a specific archive
This adds the archive jid to the query

- move it into message_archiving.py

- A Migration from last_mam_id config value is included

When we search for duplicated stanza-ids we have to do it
in the context of an account

New visible func

Closes #8670

See merge request gajim/gajim!153

Use Gio.NetworkMonitor for reconnecting

See merge request gajim/gajim!149

Add symbolic icon

See merge request gajim/gajim!151

Fix #8749: Misleading error message when joining a room

Closes #8749

See merge request gajim/gajim!150

Distinguish between 'item-not-found' and 'remote-server-not-found'

Fixes #8749

- Some plugins do not depend on gui extension points and need the
roster to be initialized

- Add more logging

According to the XEP, caps hash has to be added to all presences

Plugins maybe want to use in their activation Gajim methods that
use an extension point. But because the PluginManager Object is not fully
initialized, the extension point method is not available yet

First create the PluginManager Object, then load Plugins.

- Plugins need the possibility to add caps before Gajim updates them

- This uses also NetworkManager, but also other more low level interfaces
on linux
- This should work cross-platform
- Leave network_watcher.py for now, because it shows how
to use the Gtk dbus interface

Regression introduced in 9b866fd1