Optiq-0.6 changes.
Use Optiq parser template to generate Drill parser
a) exec/java-exec/pom.xml changes:
1. Write a plugin to move current existing codegen directory to target
   (fmpp can't handle more than one directory as template input dir).
2. Change template directory path in fmpp plugin.
3. Extract CombinedParser.jj into target/codegen/templates directory
4. Plugin to compile CombinedParser.jj using javacc

b) Add parser.tdd to define values for freemarker variables in CombinedParser.jj template
c) Use new Frameworks.getPlanner interface in DrillSqlWorker
Optiq-0.6 changes.
DRILL-392: Add support for SHOW TABLES/DATABASES and DESCRIBE TABLE.