sortmerna + sumaclust added to the open reference OTU picking pipeline

So the pre-filtering isn't even possible with sortmerna? I don't think that's a problem, but it's just not what I was expecting so want to confirm that I'm reading this correctly.

Also, this is minor, but since ``prefilter_percent_id`` is a float, you should compare against a float (i.e., ``0.0``). It won't make a difference - just stylistic.