Bump requirements for GTK+

For use-header-bar and gtk_dialog_get_header_bar().

https://bugzilla.gnome.org/show_bug.cgi?id=727063
Use header bar in the file selector dialog

https://bugzilla.gnome.org/show_bug.cgi?id=727063
Use headerbar in the prop dialog

https://bugzilla.gnome.org/show_bug.cgi?id=727063
Use headerbar in the new archive dialog

https://bugzilla.gnome.org/show_bug.cgi?id=727063
Use headerbar in the delete dialog

https://bugzilla.gnome.org/show_bug.cgi?id=727063
Use headerbar in the request dialogs

https://bugzilla.gnome.org/show_bug.cgi?id=727063
Use headerbar in the ask password dialog

https://bugzilla.gnome.org/show_bug.cgi?id=727063
Use headerbar in the passowrd dialog

https://bugzilla.gnome.org/show_bug.cgi?id=727063
Use headerbar in the test result dialog

https://bugzilla.gnome.org/show_bug.cgi?id=727063