initial-restructuring

- restructured the code
- now to add a new query to be executed, we can add a new test R file under testcases/ (in order to test particular cases like postagg/js agg/etc)
- framework will execute all the testcases sequentially
- added utility tool to generate sql for tpch_lineitem segments for a particular data size. sql can be used to add segments to coordinator segments table.