Make scitype efficient for views of CategoricalArrays

[ablaom]

This code makes scitype avoid calling expensive type unions over elements in the case of CategoricalArray's. However, it does not catch views of CategoricalArrays. So the type in the method referenced needs to be broadened.

To include views of CategoricalArrays (which are not categorical arrays) is a bit awkward, but here's the latest authority on how to do this.