Activity (5.17.0) support for HSQLDB (2.3.2).

The project, we are developing, relies on HSQLDB as a testing DB and embedded file DB. "Why not H2?" - you may ask. We suppose HSQLDB DB more stable and mature java DB. So we need builtin support for this DB from Activiti side. And we have prepared this pull-request, that cover our needs (as we can see, running your tests).