Add WINDOW clause support

Improve window clause correctness checks

Add NTILE(), LEAD() and LAG() window functions

Add experimental implementation of remaining types of window frames

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