export/hazard:

Use `iterator()` when fetching (potentially) large hazard curves, to avoid
caching them. This drastically reduces spikes in memory usage for the export.
export/hazard:

Slightly faster and slightly leaner (less memory usage) query for hazard
curve export.
export/hazard:

Updated HazardCurveData query to avoid returning and constructing millions of
Point geometry objects.
export/hazard:

When exporting hazard curves, order DB query results by `id`. This ensures
that results have a stable and consistent order.
Merge pull request #1008 from larsbutler/hc-export-optimize

Optimized hazard curve export

[r=matley] [f=1099763]
db/schema/openquake.sql:

Added `weight` to `hazard_curve_data` table. This is just copied from
`lt_realization`... when doing processing, this makes for less joins and
a simpler query.
db/models:

Added `weights` to `HazardCurveData`, to make the schema changes.
calcs/hazard/classical/core:

Added mean curve, quantile curve, and weighted quantile curve post-processing
functions.
calcs/hazard/class/core:

Cleaned up imports.
calcs/hazard/classical/core:

Added a constant to limit HazardCurveData query sizes.
calcs/hazard/classical/core:

Added a couple of utility functions for (incrementally) fetching
hazard curves for post-processing.
calcs/hazard/classical/core:

Added an alternate method for doing mean/quantile post-processing. This method
is currently not distributed.
calcs/hazard/general:

Finalization of hazard curves now inserts the `weight` also.
calcs/hazard/classical/core,post_processing:

Moved mean and quantile curve functions to `post_processing` module.
tests/calcs/hazard/classical/post_processing_test:

Added unit tests for mean/quantile curve functions.
calcs/hazard/classical/post_processing:

Added a an optimized/special-cased version of `mquantiles` for
`compute_quantile_curve`.
tests/calcs/hazard/classical/post_processing_test:

Added a comparison to scipy's mquantiles, to test the quality of the custom
optimized version (see
calcs.hazard.classical.post_processing.compute_quantile_curve).
calcs/hazard/classical/post_processing:

Corrected a comment.
removed REXD
fixes 1096889