Fix project bv curl conf

Hi,

Here's a new function to handle the Dirichlet boundary conditions for FE_Nedelec elements. It uses a fairly simple L2-projection method to compute the degrees of freedom on edges and faces. Rather than replace the current function, I've given it a new name as this may be less efficient on geometries with rectangular faces.

This also doesn't solve the issue when the face orientations are not of standard type.
Can you elaborate what exactly you mean with `L2-projection version`? I recognize that the `project_boundary_values_curl_conforming` function is not explicit which kind of projection is being used. However, if I was wondering whether I should use that or this function, it would be good to know how exactly the two functions differ.