Removing ruptures phase 2

This pull requests remove the ruptures as pickled objects from the database (bug https://bugs.launchpad.net/oq-engine/+bug/1277354). This is possible because it also removes the GMF-on-the-fly feature. Also the class models.SiteCollection can be removed now.
Notice that surface stays in the db as pickled column of the table SESRupture. They will removed in future pull requests.

For a clean diff https://github.com/gem/oq-engine/pull/1371 should enter first.