Update `template_gvec`

• Delete accidental inclusion of an empty log file.
• Add gvec_to_python dependency of numba>=0.54.0 to requirements.txt.
• In GVEC_MHD_equilibrium, use extract_2form() and set_projectors() from tensor_spline_space class.
• Check that Curl{A1} = B2, and Div{Curl{A1}} = 0 for GVEC data.
• Compute J2 = Curl{B1} and check that Div{Curl{B1}} = 0. (It's not, because B1 blows up at s=0.)