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.
docs/source:

Added risk docs to the table of contents. Previously, there were NO risk docs
at all.
calcs/risk/general:

Major docstring cleanup.
calcs/risk/hazard_getters:

Major docstring cleanup.
calcs/risk:

Major docstring cleanup (which removes a lot of warnings when building docs).
db/models:

Docstring cleanup.
calcs/hazard/classical/post_processing:

Docstring cleanup.
Merge pull request #1105 from larsbutler/char-source-rupture

Event-Based Hazard: Save multi-surface ruptures

[r=matley] [f=1144225]
Merge pull request #1107 from larsbutler/clean-up-doc

Big docs cleanup

[r=matley]
merge commit