Restructure factorization types

[brainandforce]

I think we can redefine RowHermite and ColumnHermite to be aliases of a common Hermite type with the type of the HNF matrix distinguishing between row and column forms (lower and upper triangular, respectively). Something similar can be done with the Smith type in all likelihood.

These would be breaking changes.

[brainandforce]

So I attempted to perform this refactoring using the UpperTriangular and LowerTriangular wrapper types, but I didn't realize that those types only work on square matrices (a more generic constructor would probably be called UpperTrapezoidal and LowerTrapezoidal).

Such a refactoring would either have to involve constructing our own view types or simply asserting in the constructor that the matrix is upper/lower trapezoidal as needed.