Added status_at_node property.
Added status_at_node property.

New status_at_node property to get the node_status array of a ModelGrid.
The returned array is a wrapped version of a numpy array with the
__setitem__ and __setslice__ methods overridden so that the the
ModelGrid links are updated if the node status array is changed.

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