Moved the epsilons from the getters to the database

See https://bugs.launchpad.net/oq-engine/+bug/1362479 for an explanation.
The tests are running here: https://ci.openquake.org/job/zdevel_oq-engine/647
By looking at the log, one sees for the demo risk/ProbabilisticEventBased several messages such as
`Sent 5M of data`. Before it was `Sent 400 M of data` :-)