app.nlp.mention: a redesign of the parse-based mention finder

Conll alignment precision and recall before:

precision = 0.3720178302360623
recall = 0.7998785097192225
precision = 0.3260515919126191
recall = 0.8017142857142857

and after:

precision = 0.39847752053344015
recall = 0.9397948164146869
precision = 0.34170957775489186
recall = 0.948

(yup, multiples of tens of precision gained at almost no loss in recall)