Add N1curlFenicsForm class and n1Curl_tet_mass form for testing

Commit extends the FFC build files to allow generation of a mass form for 3D for Nedelec H(curl) elements (of the first kind). It also adds the resulting form. The latter, is integrated into the HyTeG code structure by adding a corresponding class and included into the HyTeGVsFenicsFormTest to compare it to the N1E1FormMass form.