NEDELEC_ONE linear hex

This PR implements the linear hex for Nedelec element of the first type. Includes a new vector_fe_ex4 which exercises it. It seems I happened to pick a nice problem because I got 2nd order in L2 (only first order in HCurl and L2 error is expected for Nedelec elements of the first type). Thanks to @roystgnr who helped me the edge orientation consistent. Tet version "soon". There's a lot of overlap between vector_fe_ex3 and vector_fe_ex4, so it might be cleaner to merge them, but I was feeling lazy.