Combining mixed type hypotheses

[desh2608]

In its current form, DOVER-Lap does not elegantly handle the case when the input hypotheses are mixed-type. By "mixed type", we mean that some of them have overlapping segments and others do not. It seems the "label mapping" can still be used for this setting, since it uses "relative" overlaps (i.e. intersection-over-union) instead of absolute overlaps to compute speaker similarity. The problem would arise in "label voting", and this needs some new heuristics (or confidence measures) to estimate the actual number of speakers in any region.