Added _setup_node_at_cell for rectilinear graphs.
Added _setup_node_at_cell for rectilinear graphs.

csherwood-usgs/landlab,cmshobe/landlab,cmshobe/landlab,csherwood-usgs/landlab,Carralex/landlab,Carralex/landlab,ManuSchmi88/landlab,Carralex/landlab,laijingtao/landlab,cmshobe/landlab,landlab/landlab,amandersillinois/landlab,landlab/landlab,ManuSchmi88/landlab,RondaStrauch/landlab,RondaStrauch/landlab,RondaStrauch/landlab,landlab/landlab,laijingtao/landlab,ManuSchmi88/landlab,amandersillinois/landlab