Hide intro_button when user has fully interacted with it like Glade
I like that Cambalache has a similar Glade-like UI with the intro button in the header bar. But that feature is useful only once. Glade hides it and makes it easy to access again through GtkMenuButton
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And thank you for this awesome RAD tool! I was worried I'd have to manually type my GTK 4 UI files using a text editor ;P