Adapt to recent Gtk::Builder child-widget ref-counting fixes.
Field Definition: Restore some parent containers.

And change them from (deprecated) GtkAlignment to GtkBox.
Glade files: Replace (deprecated) margin-left with margin-right.
Glade files: Replace deprecated xalign and yalign.
Glade utils: Initialize widget to 0 before, not after getting it.
Glade files: Replace unnecessary use of deprecated xpad.
Glade files: Replace some more (deprecated) GtkAlignments.