Merge branch 'master' of i10git.cs.fau.de:er96apow/UGBlocks_V3

blockgrid coordinates in constructor und diffop local stiffness matrices effizienter falls constant in z-Richtung

lens creation function aufgerÃaeumt, beispiel fur fft angepasst (gerade fehler drin, verstaerkung geht nicht

added interpolator, special for surface only! faster than general interpolator, especially helpfor for interpolation of surface deformation

trilinear interpolation for grids available, but doesn't always give good results. needs to be improved