Adding second derivatives for PYRAMID13.
Add PYRAMID13 support to build_cube().
Add support for writing 13-node pyramid elements to Exodus files.

These don't seem to display properly in paraview... the issue seems to
be that, at least in the Exodus format, Paraview only reads the first
5 nodes of the 13-node element.  So it will display a mesh containing a
single pyramid just fine by ignoring all the points after the first 5,
but if there are multiple pyramids present in the file, the mesh will
be garbled.
    Adding PYRAMID13 support in miscellaneous places:
    * string_to_enum()
    * Various functions in fe_lagrange.C
    * Quadrature initialization routines
    * FEAbstract::on_reference_element()
    * lagrange_nodal_soln() helper function
    * FEAbstract::get_refspace_nodes()
    * FEInterface::max_order()
    * l2_lagrange_n_dofs()
    * monomial_n_dofs()
    * xyz_n_dofs()
    * Quality::valid()
    * ElementTypes::basic_name()
    * ElementTypes::name()
    * QGrid::init_3D()