Zeiger Cascade test & wreath product

(originally by @nehaniv )

*Implement a test for cascades to check whether they have the Zeiger property. On a path in the tree, they are constant until they permute, and then are the identity. NB: they might permute at the top, or at a leaf, or never...

*Command for the Zeiger wreath product , i.e. subsemigroup of the wreath product consisting of Zeiger cascades.
