add occurrence status = present as predicate for get_gbif_occs function

[stevenpbachman]

get_gbif_occs function should include occurrence status = absent otherwise we will be including absence records.

Example here:
https://www.gbif.org/occurrence/search?dataset_key=fca5e616-990e-4d62-adc3-3122ed64b8e8&occurrence_status=absent

Not many in GBIF yet, but will likely grow.