plotter modernization
plotter modernization

1. Update docstrings (esp. on `imshow_grid`)
2. Modernise names to LL standards (e.g., imshow_grid_at_node)
3. Deprecate old names.

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