Expand the Greenland glacier region to extend slightly beyond Greenland

In discussing the changes I'm making for #423 with @gunterl and @Katetc , Gunter raised some concern about not having any SMB beyond the Greenland land area, if someone wanted to do a run that allows the formation of ice shelves around Greenland.

After some discussion, we agreed that best thing to do long-term is probably to do a slight expansion of the Greenland glacier region on CTSM's surface dataset to accommodate possible/likely ice shelf expansion. However, this needs to be done carefully to avoid including much additional land (like Ellesmere Island) in this mask. (If Ellesmere Island is treated the same as Greenland, it can generate ice runoff that, at least in the past, has resulted in problematic runaway sea ice growth.)

(An alternative would be to go back to having an extra region for this purpose, but our feeling was that that's a less good approach, given that there aren't any great combinations of glacier region behaviors that can be applied to that region besides those that are applied to Greenland itself, so it would make more sense just to expand the Greenland region rather than re-introducing a separate, small region.)