Add FIRST_VALUE(), LAST_VALUE(), and NTH_VALUE()

Add ROW_NUMBER(), RANK(), DENSE_RANK(), PERCENT_RANK(), and CUME_DIST() window functions

Bugfix - Release MVStore lock and file resources rightly even if errors when compacting database

Reset aggregates before reuse

Add experimental support for aggregates with OVER (ORDER BY *)

Evaluate window aggregates only once for each partition

Move more code from Aggregate and JavaAggregate to AbstractAggregate