Indexes in TPC-W.

* Added a configuration parameter to the Populate servlet named USE_INDEXES.
* Changed DML to always have indexes, not using them presents no overhead.
* The TPC-W App uses the indexes accordingly to the parameter passed during the population.
Merge pull request #4 from nmldiegues/develop

Indexes in TPC-W.

  See log for commit 097f8281fc6a43e0d60cbb0ace8ec4cf6655f665.