Better names for the classes of categories

[leftaroundabout]

When I first wrote the hierarchy, I didn't take good care to pick names that match the underlying mathematical terms. Thus, for example, Cartesian describes a symmetric monoidal category. Morphism doesn't have any more to do with morphisms than any of the other classes.

This keeps bugging me again and again. I will rename the classes some time later this year (hopefully).

Anybody who wants to chime in on what particular names to choose, feel free. I do still want to retain almost-compatibility with base:Control.Arrow, but it's perhaps not that important.