Perform factor reduction as a modular step

Adds a fourth step of modular processing. After event processing, matching and
analysis are completed, factor reduction is performed through a module. At the
moment there is only one such module, the accuracy-based factor reduction that
was already present, but new modules can be added and selected through a
command line option.

Signed-off-by: Benjamin Poirier <benjamin.poirier@polymtl.ca>