db/schema/openquake.sql:

Added a field to store/cache a pickled SiteCollection object in the
`uiapi.hazard_calculation` table.
db/models:

Added `site_collection` field to the HazardCalculation model.
db/models:

HazardCalculation now interally caches `points_to_compute`.

Previously, this was only cached inside calculator objects.
calcs/base: Corrected a comment
calcs/hazard/general:

Remove computation mesh caching from the base hazard calculator, since this
caching is now done within the model (`HazardCalculation`).
db/schema/security.sql:

Added UPDATE permissions to `hazard_calculation`.
db/models:

Added a missing import to make `site_collection` creation/caching work.
calcs/hazard/classical/core:

Classical calculator now uses the cached SiteCollection in tasks, instead
recomputing it every time.
calcs/hazard/disagg/core:

Disagg hazard calc now uses the cached SiteCollection.
calcs/hazard/event_based/core_next:

Event-Based hazard calc now uses the cached SiteCollection.
calcs/hazard/scenario/core:

Scenario hazard calc now uses the cached SiteCollection.
calcs/hazard/classical/core:

Classical calculator now caches the site collection during pre-execute.
calcs/hazard/event_based_core_next:

Event-based calculator now caches the site collection during pre-execute.
calcs/hazard/disagg/core:

Disagg calculator now caches the site collection during pre-execute.
calcs/hazard/scenario/core:

Scenario calculator now caches the site collection during pre-execute.
tests/calcs/hazard/classical/core_test:

Test that the site collection is cached during pre-execute.
tests/calcs/hazard/disagg/core_test:

Test that the site collection is cached during pre-execute.
calcs/hazard/general:

Removed `get_site_collection` from hazard/general.
db/models:

Moved `get_site_collection` to db/models.
db/models:

Fixed a reference to the `SiteData` model class.