StViewport (custom grid, part 4)
St has the regular abstractions to handle actors that are bigger than their parent could handle: StScrollable, StScrollView, and StAdjustment.
However, the only StScrollable implementation available currently is StBoxLayout, which forces a ClutterBoxLayout as the layout manager (and relies on it not being unset).
Introduce StViewport, which is a minimal StScrollable implementation that doesn't rely on any specific layout manager.
Edited by Georges Basile Stavracas Neto