MentionEntityType annotation in NerAndPronounMentionFinder

adding stuff in NerAndPronounMentionFinder to add MentionEntityTypes directly, since the Ner tagger already produced types. This also adds MentionEntityType as a postAttr for this annotator. Note that new asymmetry between this annotator and the parse based mention finder, which does not have such a postAttr. Note that NerAndPronounMentionFinder can have either Conll or Ontonotes Ner has a prereq, but MentionEntityType requires an Ontonotes Ner tag. I convert Conll "PER" to Ontonotes "PERSON." Otherwise, nothing has to be translated (although there are certain tags in the MentionEntityTypeDomain that you'll never predict if you use Conll NER).