Serialization of certainty ratings

[dlschwartz]

@wsalesky See 8559-387. The current serialization is grabbing tei:note[@type="certainty"] as the rdfs:label and rdfs:desc for the factoid. Instead it should be grabbing tei:event/tei:desc.

Rather than grab the text node of tei:note[@type="certainty"], we should instead grab tei:note/@subtype. We don't currently have an item in the taxonomy for the uncertainty ratings, but we will eventually. If we take the value of @subtype and append it to "swd:keyword/" that should give us what we need. The result should be:

[statement instance] spq:certainty swd:keyword/incerta ;