Changed so that links and cells keywords can be grid objects.
Changed so that links and cells keywords can be grid objects.

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