calcs/hazard/classical/post_processing:

Added `make_uhs` function to compute UHS from hazard maps.
tests/calcs/hazard/classical/post_processing_test:

Added a test for `make_uhs`.
db/models:

Implemented `__str__` and `__repr__` for HazardMap. This makes debugging, etc.
nicer.
calcs/hazard/classical/post_processing:

Added `_save_uhs` function for saving UHS results to the DB.
calcs/hazard/classical/post_processing:

Added `do_uhs_post_proc` function for performing the uhs computation for a
given job.
calcs/hazard/classical/core:

Hooked in the uhs post processing to the `post_process` method of the
classical calculator.
tests/calcs/hazard/classical/core_test:

Added a light test to check that hazard maps and UHS are produced in the
classical workflow.
tests/export/hazard_test:

Updated copyright date in license header.
tests/export/hazard_test:

Updated `test_classical_hazard_export` with the correct number of result
artifacts.

I'll need to update the test to exercise the UHS export as well, once it is
implemented.