Removed hazard curve progress

This PR rewrites the classical calculator as a map reduce job, so that the temporary table hazard_curve_progress (the one that was giving locking issues in situations of strong concurrency) can be removed. See https://bugs.launchpad.net/oq-engine/+bug/1256471 for the details.

The performance is roughly the same as before, except in the cases where the locks made the diffence, in which case it is faster.

The tests are green: http://ci.openquake.org/job/zdevel_oq-engine/208