sparse meshgrid evaluation, set_projectors in spline_space
- evaluation of sparse meshgrid output now possible in spline_space evaluation routines
- added set_projectors function in spline_space --> projectors are now part of the spline_space object
- set_extraction_operators 1d removed in struphy code (mass_matrices_3d_pre)
- test projection of random spline function on other de Rham spaces