Make GVEC tests work with new STRUPHY code

• Remove internal dependence on gvec_to_python package.
• Rename xx_test_template_gvec.py.
• Replace default GVEC data with updated version.
• Implement params_map for kind_map=='spline'.
• Update .gitignore to exclude build folders.
• Remove gvec_to_python references in Makefile.
• Update default GVEC data path in xx_test_template_gvec.py.
• Correct if eta3 == None to if eta3 is None in domain_3d.py.
• Provide empty params_map for spline map in domain_3d.py.
• Pass spline coefficients to domain_3d via a hdf5 file.
• Update test_divB.py.