Added pfr_cut, throats, targets, fixed speed issue

Added x_aligned_edges and y_aligned_edges
Added pfr_cut, outer_throat, inner_throat, outer_target, inner_target
Fixed speed issue with search_edges. Needed to remove use of Sets
Made code bit more clearer by using nodes, cells, edges as name of
)D, 1D and 2D ibjects (instead of going for o1.object etc.)
Attached neighbours in each cell boundary