This removes the emptyLayoutMod method from the LayoutModifier class, and
change the Stack parameter to redoLayout to a Maybe Stack one. It also changes
all affected code. This should should be a refactoring without any change in
program behaviour.
This patch includes several changes, which are strictly related and
cannot be recorded separately:
- remove Decoraion.isDecoartion and introduce Decoration.isInStack
(with the related change to LayoutHints)
- in Decoration introduce useful utilities: isVisible, isInvisible,
isWithin and lookFor'
- MouseResize: - invisible inputOnly windows will not be created;
- fix a bug in the read instance which caused a failure
in the state deserialization.
