ScalarEq: Implement modal Bspline2 DG evolution

Similar to !207 (merged), but using the new 2nd order Bspline basis.

Currently supports only bare evolutions and no HRSC etc.

Also: This is a quasi-nodal Ansatz similar to the Bernstein Ansatz, i.e. it is not interpolating, but the modal coefficients are related to some sampling of the data on the grid. This means that one has to sum the modal coefficients onto the grid to obtain the nodal values, which can be done with interpolate or a Vandermonde matrix. Atm this is not consistently done in the ScalarEq project, hence, care needs to be examined when interpreting results!