Change grid interpolation and order

[termi-official]

It is often beneficial for mechanical problems to have a grid with the same interpolation as the displacement field. This is usually "just" a change in order of the required interpolation. The simplest hack here would be to just create a dof handler and use the nodal dofs to generate the new nodes of the grid. It should be noted that at the time of writing this (~v0.4.0) we rely on Lagrange-type interpolations for the grid to make the dof management functional.