Changed deprecation for lambdify matrices

This commit changes how lambdify behaves, mostly having to do with the
deprecation plan to change the default from Matrix -> numpy.matrix to
Matrix -> numpy.array.

- No longer have the `default_array` kwarg. Everything is solved by
  passing in a custom dict for the `modules` kwarg.

- Throw warning only if expr is a matrix, and the translation for
  `Matrix` hasn't been set at all by the user. If it has, no warning
  is thrown, as the translation is intentional.