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.
tests/db/models_test:

Moved tests for `get_site_collection` this module.
tests/calcs/hazard/general_test:

The `get_site_collection` tests have been moved to `tests/db/models_test.py`.