Move datasource creation to this module debiki-dao-rdb.
Revert "Move datasource creation to this module debiki-dao-rdb."

This reverts commit bc43411aa03a43bae272e142b0cfe0931917e3cd.  Reason:
play-jdbc depends on Play Framework and having a running Play application,
which makes it seemingly very complicated to start the db test; for example,
the Play app seems to start ElasticSearch, don't know why, boring.