Adapted getting Surface Normal from Level Set Function s.t. normal has length = orthog. distance to surface.

Changed distance in placing of mirror particles. Now, normal vector should have length = distance to the surface.

Merge branch 'new_sussman_enoweno' of https://git.mpi-cbg.de/openfpm/openfpm_pdata into new_sussman_enoweno

Changed structure of templated functions in Eno/Weno s.t. it can be used with less params. Adapted UpwindGradient accordingly.

Changed gradient type from double[dims] to Point<dims, double> because preferred by Paraview and because Point has already a function norm, s.t. getting the gradient magnitude doesn't require an extra function.