Landice/script updates

[matthewhoffman]

A number of minor updates to scripts used in landice grid workflows.

• Correct error in numCells method in cullMask script
• Make Glimmer vertical spacing the default option when making new meshes
• Correct an error check in the interp script preventing nearest neighbor interp from working for two MPAS meshes
• make Gt default units in globalStats plotter