Add computation for minimally reproducible sets

Add computation for minimally reproducible sets

A minimally reproducible set of a configuration
is simply the smallest set of events whose
collective histories joint together cover every
event in the configuration. Effecively, it is
the maximal set of C whose history equals C.

The computation builds upon the maximal_subsets_iterator
introduced in a prior phase and exploits all of
the work that already went into computing the
subsets