Minor code change due to Optiq 0.6-SNAPSHOT change.

Rename ConnectionConfig to DrillConnectionConfig due to optiq-0.6-SNAPSHOT add an interface with same name.

Signed-off-by: vkorukanti <venki.korukanti@gmail.com>
More minor changes due to Optiq 0.6-SNAPSHOT:
1. org.eigenbase.rel.Direction capitlization changes
2. DrillAggregateRel and DrillProjectRel interface changes
3. SqlExplain interface changes
Copy of Optiq's Sql parser file
SHOW TABLES/DATABASES, DESCRIBE TABLE (wip)
1. Need to improve the testcases to verify the results
2. Extend DESCRIBE to handle schema.table.