[Lazarus] Undo/Redo in Form Designer

[Juha Manninen]

I am still thinking of the most important case: undo for delete operation.
It is also the most difficult one. Anchors and alignment depend on the
order of creation. It is not enough to just insert a deleted control
back. Maybe the whole form must be recreated. Maybe there must be a
snapshot history of the form.

I guess Mattias must comment on your code at some point. I cannot say
whether it fits the big picture when undo for delete is implemented.

Juha