Remove regional duplication in tables GIA and GIG

[durack1]

The Antarctica and Greenland regional dupe tables should really be collapsed into a single table (Glacial Ice)GI vs the GIA and GIA that is currently included. It would be possible to use a region-specific grid_label to then identify differences in grids/regions.

This is worth thinking about, so opening up a dedicated issue to start dialogue.

@taylor13 @matthew-mizielinski pinging you both

[taylor13]

See #6 for how we could distinguish different regions and area types. This would indeed make it possible to remove duplicate tables.

[taylor13]

Under my proposal, the organization of "tables" is rather unimportant. (see https://docs.google.com/document/d/1FHqbU2qikt92mApcaEgYY-10O2_oJrTWK_pO4omwpo8/edit ) There is a single list of variables, and then these can get organized into tables however the data requester and/or the data writer want to organize them. An example of a partial table that might be built on the "master list" of variables is shown in this appendix. Only the master list of variables would be centrally curated to prevent duplication and errors. The tables built on top of it could be maintained by individual projects or modeling centers, but all variables in those tables would have to be extracted from the master list (and, of course, they could propose variables be added to the master list).