Angular Quadrature should provide angular or Cartesian values

[jsrehak]

Classes derived from AngularQuadratureSet should provide the ability to retrieve the quadrature points in the format (x, y, z) as well as (theta, mu).

This could be achieved through functions called cartesian_quadrature_points returning a map of QuadraturePoint<dim>, and angular_quadrature_points returning a map of QuadraturePoint<dim-1>. For dim == 1, the angular should either return the same thing or perhaps a runtime error.

Labeled major due to a required interface modification.