NHLIB Integration: Update Hazard Curve Schema (DB and NRML)

[Lars Butler]

With the integration of NHLIB, we need to add a few attribute the hazard curve schema. This involves changes to the NRML XML schema as well as the DB schema. (Both schemas should be roughly equivalent.)

Here's a sketch of what the new NRML schema could look like: http://pastie.org/4126533

The DB schema needs the following changes.

hzrdr.hazard_curve:
  - lt_realization_id (optional if statistics != NULL)
  - investigation_time
  - statistics (mean, quantile, or NULL)
  - quantile (only use with statistics == quantile)
  - imt
  - imls
  - sa_period (only use with imt == “SA”)
  - sa_damping (only use with imt == “SA”)

hzrdr.hazard_curve_data: No changes required.

[Lars Butler (lars-butler)]

First pull request: https://github.com/gem/nrml/pull/32

[Lars Butler (lars-butler)]

Pull request for the DB schema changes: https://github.com/gem/oq-engine/pull/802