sql_io.py: Added import_csv()

csv2db: Don't truncate the table before loading rows because it has just been created, and is therefore empty. This statement may be left over from a time when the table was created only once, and its creation was not rolled back if the import fails.

sql_io.py: cleanup_table(): Print 'Cleaning up table' log message

sql_io.py: cleanup_table(): Also vacuum and reanalyze table

tnrs_client: Use new tnrs.tnrs_request()

Added tnrs.py

tnrs_client: Factored TNRS request code into separate function tnrs_request()

inputs/VegBank/taxonimportance/map.csv: Documented that taxonimportance is not 1:1 with taxonobservation

mappings/VegCore-VegBIEN.csv: Removed unnecessary /_first/# suffix for multiple terms in the same _exists expression, because _exists() only checks whether its node is non-empty, and it does not matter how many child nodes it contains

schemas/vegbien.sql: taxonoccurrence: taxonoccurrence_unique_within_locationevent unique index: Fixed bug where locationevent_id needed to be enclosed in COALESCE so that the unique constraint also applies to rows with NULL locationevent_ids (there is no other unique constraint handling these rows)