sql.py: create_table(): Don't set pkey.nullable to False because the caller should make sure the pkey has the appropriate type

csv2db: Use sql_gen.TypedCol.nullable instead of manually adding 'NOT NULL' to the type. Ensure that pkeys are properly NOT NULL.

csv2db: Adding indexes: Create plain indexes using ensure_not_null=False because the indexes will primarily be used by the user to search for specific values, rather than by the mapping script which uses the ensure_not_null

sql.py: DbConn.col_info(): Run query with log_level=4 because it gathers information about database structure, and should have the same log_level as other queries that do that

csv2db: Adding indexes: Fixed bug where col.to_Col() could not be used because sql.add_index() does not support name-only columns (plain strings are OK, though)

sql.py: create_table(): has_pkey: Use new TypedCol.constraints to store 'PRIMARY KEY'

sql_gen.py: TypedCol: Added constraints instance var

sql_gen.py: EnsureNotNull: Made coalesce() all uppercase to match how pg_dump spells it

schemas/vegbien.sql: namedplace: Fixed bug where parent_id needed to be included in UNIQUE CONSTRAINT (now UNIQUE INDEX), since there can be more than one e.g. city of the same name if they are in different states

schemas/vegbien.sql: plantname: Changed indexes to use `COALESCE` to match what sql_gen now does