add scores/stats for subject/object

[nlwashington]

I would like for all nodes to have some summary stats attached to them for us to perform some downstream enhancements on...

minimally, this would be the IC score for any ontology node, but in the future we could look at storing some other things like the annot sufficiency score on other node types, or perhaps the min/max/sum of the annotations for annotated nodes like genes/genotypes (though those could be computed on the fly if we had the IC).

we could start by simply adding a subject_ic and object_ic. alternatively, @cmungall should the "quad" just be updated to be a "quint" to have the IC always part of it?