Add global refinement for mixed-topology and higher order meshes

[chrisrichardson]

Add a mesh refinement routine for mixed-topology and higher-order meshes:

• [ ] refine higher-order tetrahedra (need to change geometry, but topology should be same as for P1)
• [ ] global refinement of hex, pyramid, prism meshes

[jorgensd]

2D refinement routines would also be nice (quad, tri) and easier to debug).