fix: schemas/util.sql: materialize_query(): 1st param should be named table_, not view_

schemas/util.sql: added drop_view()

schemas/util.sql: added materialize_query()

validation/aggregating/*/*.sql, schemas/vegbien.sql, lib/runscripts/validations.pg.sql.run, inputs/bien2_traits/validations.sql: added _ to beginning of each view name so the validation views would sort at the top in the datasource's tables list. this will also make the validation result sets easily distinguishable from the data tables.

schemas/util.sql: ifnull(): use COALESCE instead, because it turns out that MySQL's IFNULL is just a special case of this

schemas/util.sql: added ifnull(), equivalent to MySQL's IFNULL (Postgres auto-lowercases the name)

schemas/vegbien.sql: public_validations_*: merged into single public_validations schema, with type-specific prefixes for each query, so that datasources can use validations queries from multiple type categories, and so that each datasource doesn't have to indicate which validations output schema it's using

schemas/util.sql: diff_cols(): documented how to run EXPLAIN on the FULL JOIN query

schemas/util.sql: diff_cols(): embed left_query/right_query directly in the main SQL statement, so that the query planner can take the sort order of the queries into account in planning the FULL JOIN (and where possible, use a fast merge join)

schemas/vegbien.sql: regenerated from DB, which adds an autogenerated column alias