calcs/hazard/disagg/core:

Use `self.block_size()` instead of accessing the config parameter directly.
openquake.cfg:

Added `point_source_block_size` to sample config file.
calcs/hazard/general:

Added `point_source_block_size` helper method to the base hazard calc class.
calcs/hazard/general:

Call `self.block_size()` instead of getting the block size via the config
file.
calcs/hazard/classical, disagg, general:

Moved basic `task_arg_gen` implementation to the base hazard calc
and refactored it to include support for `point_source_block_size`.
openquake/engine, tests:

Renamed `CalculatorNext` to `Calculator` and `BaseHazardCalculatorNext` to
`BaseHazardCalculator`.
calcs/hazard/general:

Moved some DB query statements in `task_arg_gen` to separate methods
to make things easier to mock and test.
calcs/hazard/event_based/core:

Updated `task_arg_gen` to split point sources into blocks of the correct size.
tests/calcs/hazard/general_test:

Added a test to exercise the logic of `BaseHazardCalculator.task_arg_gen`.
tests/input/source_test:

Fixed a slow test. It went from ~20 seconds runtime to less than 1.
calcs/hazard/event_based/core:

Removed the `n_sources` counter. It wasn't used in production.

It was referenced in one test, but it was used in a way that didn't make
sense.
tests/calcs/hazard/event_based/core_test:

Removed an assertion referencing the `n_sources` variable, which has been
deleted.
calcs/hazard/general:

Order results by id in `_get_realizations`.
calcs/hazard/event_based/core:

Use `_get_realizations`.
tests/calcs/hazard/general_test:

Renamed some test mock objects for better clarity.
tests/calcs/hazard/event_based/core_test:

Added a test for the `task_arg_gen` logic of the event-based calc.
tests/calcs/hazard/general_test:

Removed an obsolete test case. It was really slow, too.
openquake.cfg:

Corrected a comment.