Merge pull request #7 from OHI-Science/master

synching ohiprep jules32 repo
Used gapfill_georegions.r to assign soverign gapfilling: finished layers 'wgi_all' and 'ss_wgi'.
additional comments in data_prep.r
additional notes
Merge pull request #71 from jules32/master

used gapfill_georegions() for sovereign gapfilling (wgi layers)