Gh 67 havingjoinsupport

- Utilize ECL HAVING function as recommended by Gavin.
- SQLFragment.getValue() incorporates special translation for fragments
    of a Having clause in which the ECL 'ROWS' syntax is generated.
- Grouping clauses without having clauses are still processed as part of the
    final result TABLE call for performance reasons.
- In ECLEngine, select structure is now based on the latest DS name (logic moved to a separate method).
    - SQLParser found to be upcasing group by clause, thereby creating issues for Group by having clauses.