Merge pull request #1104 from larsbutler/fix-loss-curve-export

Fix loss curve export

[r=matley] [f=*1157072]
demos/event_based_hazard/source_model.xml:

Added a multi-surface characteristic source.
db/models:

Added multi-surface support to SESRupture.
db/schema/openquake.sql:

Added `is_multi_surface` field to `ses_rupture` table.
demos/event_based_hazard/source_model.xml:

Updated planar surface point ordering to be consistent with nrml schema and
hazard lib.
db/models:

Corrected ordering of planar surface corner points.
db/models_test:

Update to test according to the change in the order of planar surface corner
points.
calcs/hazard/event_based/core:

Added support for saving ruptures originating from a multi-(planar-)surface
characteristic source.
tests/export/hazard_test:

Updated the expected number of GMFs. There are more now because we added
one additional seismic source (characteristic multi-surface) to the model.