Added a test of a custom container in GTK+. This will lead to the one that will be used by package ui.
Added a test of a custom container in GTK+. This will lead to the one that will be used by package ui.

andlabs/misctestprogs,andlabs/misctestprogs,andlabs/misctestprogs,andlabs/misctestprogs,andlabs/misctestprogs,andlabs/misctestprogs