mappings/DwC2-VegBIEN.specimens.csv, VegCSV-VegBIEN.specimens.csv: Split occurrenceID into occurrenceID and individualID, where individualID refers to the plant in plots data and occurrenceID refers to the specimen in specimens data. This prevents plant sourceaccessioncodes from being mapped to the specimenreplicate, which was messing up stems mappings for the parent plantobservation. It also avoids mapping the specimenreplicate sourceaccessioncode to additional tables where it isn't needed. (Note that occurrenceID is needed for location to ensure that each specimen gets its own location to make locationdeterminations on. Everything else is directly or indirectly scoped by location when its own sourceaccessioncode isn't specified.)