sql.py: DbConn.DbCursor.execute(): Removed no longer used params parameter

sql.py: with_autocommit(): Use isolation_level attr and set_isolation_level() method of connection instead of autocommit attr to support older versions of psycopg2

sql.py: DbConn.DbCursor.execute(): Only fetch all rows for empty SELECT query, to support older versions of Python that would give a "no results to fetch" error for other types of queries

csv2db: When reraising exception, use `raise` instead of `raise e` to preserve whole stack trace

sql.py: Removed no longer used _query_lookup()

sql.py: DbConn: Cache queries without params, as params are no longer used

sql.py: DbConn.is_cached(): Removed no longer used params parameter

sql.py: Removed no longer used run_raw_query()

sql.py: run_query(): Call db.run_query() directly instead of via run_raw_query()

sql.py: DbConn.run_query(): Removed no longer used params parameter