tests/data:

Test files for exercising pre-calculation filtering of sources when generating
task work.

In this test job, there is a single site of interest for the computation and 2
point sources. Once the point sources are dilated to the integration distance
(maximum_distance) of 180 km, one of them intersects with the point of
interest, and the other does not.

This way we can clearly test that filtering is working and that we only
generate tasks/work for thos sources in the model which are close enough.
Side note: The tasks/work are determined by the records inserted into
`source_progress`.
calcs/hazard/general:

Implemented pre-calculation filtering of sources which are too far from the
calculation area of interest.
calcs/base:

Cleaned up some documentation.
calcs/hazard/general:

Removed an obsolete comment.
calcs/hazard/general:

Fixed a PEP8 issue (line too long).
calcs/hazard/general:

Cleaned up some nested transactions. A few tests were hanging; this fixes
that.
calcs/hazard/general:

Fixed a small PEP8 issue (line too long).
calcs/hazard/general:

Added some more detailed documentation to the docstring for
`initialize_source_progress`.
tests/calcs/hazard/classical/core_test:

Fixed a typo.
calcs/hazard/general:

Added ORDER BY clause to a query to get consistent results.
calcs/hazard/classical/core_test:

Fixed some broken tests due a change in `source_progress` record creation.
calcs/hazard/classical/core:

Optimization: Don't bother updating `hazard_curve_progress` records when the
result matrix contains all zeros.
tests/db/models_test:

Added another assertion to GmfSetIterTestCase.test_iter to check first the
length of the expected and actual values to make sure they are the same.
tests/calcs/hazard/general_test:

Added a test case for pre-calculation source-site filtering.
calcs/hazard:

Remove source-site filters for classical and disaggregation calculators; this
filtering is now done pre-calculation so there's no need to do the same
distance/intersection calculations again.
Revert "calcs/hazard:"

This reverts commit 5a68bfa21dcc61f94bd400e5ecb2419f4649dceb.