Add fieldaligned output in interpolate_in_3d
Add fieldaligned output in interpolate_in_3d

this could also be a good way for smoother 3d plots since paraview
now interpolates along the fieldlines

feltor-dev/feltor,feltor-dev/feltor,mwiesenberger/feltor,feltor-dev/feltor,mwiesenberger/feltor,mwiesenberger/feltor,feltor-dev/feltor,mwiesenberger/feltor