Port screensaver listening to GTK dbus

Closes #8836

See merge request gajim/gajim!183

Fix string for a better translation

See merge request gajim/gajim!185

xgettext: Additional keyword for translatable strings

See merge request gajim/gajim!184

Remove obsolete network_watcher

See merge request gajim/gajim!182

Port music_track_listener to GTK dbus

See merge request gajim/gajim!172

- Only pass args to logging function
- Dont use 'size' as global var, its again used later in methods
- Fix a missing arg in __parse_font_size_cb()

- Get rid of deprecated Gdk.Screen methods
- remove support for 'ex' unit - not easily correct implemented and not commonly used

Fixes #8491

4.3.0 compiles fine on msys2, later version current not.

Fixes #8834

If the VCard contains a <PHOTO/> tag this is parsed as {'PHOTO': ''}

this throws: TypeError: string indices must be integers

Add support for XEP-0368

See merge request gajim/gajim!177

Fixes #8801

On destroy() the window that was last focused gets the focus
again. if destroy() is called from the StartChat Dialog, the new
ChatControl is not yet focused, because present() seems to be asynchron,
at least on KDE, and takes time.

set_active_tab() already calls present(), no need to call it afterwards
again

Refactor some Tooltips

See merge request gajim/gajim!180

Add ad-hoc commands for Groupchats

Closes #8819

See merge request gajim/gajim!179

- Dont create a Tooltip window
- Just return the tooltip grid, so we can use it with set_custom()

We dont needed anymore

Fixes #8819

Dialogs: Use get_widget_for_response() to access buttons

See merge request gajim/gajim!178

 - Use xmpps-client SRV records
 - Use separate host entry per connection type
 - Replace 'connection_types' with 'allow_plaintext_connection' option

The get_action_area() API is deprecated and under some circumstances
the wrong button gets accessed.

Fixes #8810

Also remove mam_start_date migration.
mam_start_date didnt exist in Gajim 0.16.x and it doesnt hurt
if people who used the dev version download some extra messages.
Our deduplication algorithm should take care of it.

GUI interface: fix resource warning

See merge request gajim/gajim!175

Zeroconf: fix unexpected keyword argument

See merge request gajim/gajim!174