Avoid deprecation warnings 1: alignment and padding

This is the beginning of fixing the deprecation warnings I started working on.
As discussed in #58 (closed), the idea is to use GTK+ 4 compatible tools, so as not to do this twice.
To check this, I referred to the version 3.99 documentation, available here: https://developer.gnome.org/gtk4/

This MR handles objects related to alignment and padding: GtkMisc, GtkAlignment, GtkTable and GtkVBox.
These changes should be virtually invisible.
I will open another MRs for the rest, limiting myself to that here.

Indeed, fixing these deprecation warnings can cause regressions.
So I think we should try to push to master easily reversible commits, but not too much, so as not to flood the commit history (each MR can contain a sub-history for details).

So I'm going to try to do this…
Comments and criticism on how to fix deprecation warnings and how to manage the commit history are welcome.

Thanks!