schemas/vegbien.sql: taxonconcept: taxonconcept_required_key: Added creationdate as an allowable minimum field when parent_id (containing the associated hierarchical concept) is specified

schemas/vegbien.sql: taxonconcept: taxonconcept_required_key: Removed family and genus because these are now cached fields only, and are not used for scoping a taxonconcept. Instead, *taxonomicname and taxonname+parent_id are used for this purpose. This removes several leaf taxonconcepts with insufficient scoping information to create a taxonconcept separate from the main tree. With the upcoming population of creationdate, some of these taxonconcepts will reappear due to the date's additional distinguishing information.

schemas/vegbien.sql: taxonconcept: Added creationdate (the date the taxonconcept was created or defined), and include it in the taxonconcept_unique unique index

schemas/vegbien.sql: taxonconcept: Added comment with the definition of a taxon: "a group of one (or more) populations of organism(s), which a taxonomist adjudges to be a unit" (http://en.wikipedia.org/wiki/Taxon). This is useful in clarifying that our taxon concepts are intended to serve a similar purpose, by storing one person's defined taxon.

schemas/vegbien.sql: taxonconcept: taxonconcept_required_key: Removed family and genus because these are now cached fields only, and are not used for scoping a taxonconcept. Instead, *taxonomicname and taxonname+parent_id are used for this purpose.

schemas/vegbien.sql: taxonconcept: Moved identifyingtaxonomicname near other full-taxonomic-name-related fields, after the fields that contain just the current level's component of the full name

schemas/vegbien.sql: taxonconcept.canon_taxonconcept_id: Changed four-level hierarchy to use "parsed concept" and "matched concept" instead of concatenated and parsed, because the directly-parsed name components actually go in level 2 of the hierarchy (the TNRS input name), while the name components based on the matched taxon concept go in level 3

schemas/vegbien.sql: taxonconcept.parent_id: Documented that while a taxon name may have multiple parents, a taxon concept has only one, based on the creator's opinion of where that taxonconcept goes in the taxonomic hierarchy

mappings/VegCore-VegBIEN.csv: taxonconcept: Moved infraspecific taxonconcept to its own level, rather than combining it with the level that contains the full taxonomic name and author (as well as any morphospecies), for consistency with the storage of other ranked taxonomic name components, which each get their own taxonconcept. The infraspecific taxon concept is general to all parties making idenfitications (within a datasource), while the concatenated name and author and any morphospecies are specific to the person who defined the taxonconcept used by a taxondetermination.

schemas/vegbien.sql: taxonconcept: Removed no longer used higher- and infraspecific taxonomic rank fields because these terms are now stored in their own taxonconcepts. family, genus, and species have not been removed because these are used to cache names of parent taxa for fast access by analytical_db_view.