This fixes issue #632

This also adds more consistency with the heuristic version of the code.

This is a significant refactoring of the statistical inference code,
with many cleanups and improvements, and is aimed towards future
extensibility.

The old community module is available as 'community_old' and will be
completely removed in the near future.

This fixes some strange bugs where deterministic position updates lead
to strange artifacts.

The object may be globally reset via the seed_rng() function.