mappings/DwC2-VegBIEN.specimens.csv: occurrenceID: Added VegCSV mappings for it

mappings/DwC2-VegBIEN.specimens.csv: mappings to /location/sourceaccessioncode: Added _alt to prioritize them properly

inputs/UNCC/maps/DwC.specimens.csv: herbarium: Fixed mapping to go to institutionCode instead of collectionCode

mappings/DwC2-VegBIEN.specimens.csv: Remapped institutionCode/collectionCode/catalogNumber location mappings to location.authorlocationcode

schemas/vegbien.ERD.mwb: Reset methodtaxonclass lines so that only one needs to be repositioned after syncing with the schema

mappings/VegCSV-VegBIEN.specimens.csv: locationID: Removed mapping to locationevent.sourceaccessioncode, because locationID relates to the plot, not the plot event. (The locationevent is scoped by the location when the sourceaccessioncode and authoreventcode are not specified, so duplicate elimination will still occur correctly.)

mappings/DwC2-VegBIEN.specimens.csv: Mapped locationID, for mergability with VegCSV

mappings/VegCSV-VegBIEN.specimens.csv: plotName: Removed authoreventcode mapping because plotName relates to the plot, not the plot event. (The locationevent is scoped by the location when the authoreventcode is not specified, so duplicate elimination will still occur correctly.) Instead map only authoreventcode-related fields (currently CVS's authorObsCode) to authoreventcode, via DwC's (confusingly-named) fieldNumber ("An identifier given to the event in the field").

schemas/vegbien.sql: locationevent: locationevent_unique_within_location: Added authoreventcode to index. It was already in the locationevent_unique_within_*parent*_by_authoreventcode index, but also needed to be in the no-parent (non-subplot) index. This fixes locationevent duplicate elimination when a locationevent sourceaccessioncode is not specified.

schemas/vegbien.sql: location: location_unique_within_datasource unique index: Added COALESCE and `WHERE sourceaccessioncode IS NOT NULL` now that sourceaccessioncode is nullable. Renamed location_unique_within_datasource and location_unique_authorlocationcode to location_unique_within_datasource_by_... to show that both are alternatives for globally unique keys. schemas/vegbien.ERD.mwb: Moved elements slightly to reduce the number of lines that need to be repositioned after syncing with the schema.