restructured grid
DONE:
-grid does now the init of the grid (makes sense, right?)
-loop_init labels all the loops
-grid_class is not universal anymore, since it's faster to use the neighbor pointer instead of the vector_lookups
-check ./benckmark/periodic structure.txt for data
-the shared_ptr slowed down the access, therefor removed
-all files adapted to new grid
-measure_periodic_accsess_2.cpp deleted
TODO:
-error for false init?
-loop in two_bond_update
-find a efficient system for the check-variable