reduce extensionality of fdFold to a commutativity lemma about fold_right (on lists) and permutations (of lists)

srengthen the induction principle and show euqalities such that the characterization of fdFold can be shown using fdRect

move CMRA to its own file, in anticipation ofn a dependency to SPred that would otherwise have induced a cycle

now that preoType already covers compatibility with a setoid, pcmType does not have to do that anymore

avoid being a delta-reduction away from Setoid's equiv (WARNING: some stuff doesn't compile anymore)

improve n[] notation for nonexpansive maps: the proof of Proper is no longer required, it can be derived from nonexpansiveness