Update dependencies, gazetteer, and models

[ahalterman]

This PR resolves some small issues but mostly updates Mordecai to work with newer versions of its dependencies, including Keras/tensorflow and spaCy.

Specifically

• updates the Geonames gazetteer and switch host
• updates spaCy to 2.3 (resolves compatibility with spacy 2.1 #69)
• updates Keras/Tensorflow version and retrains the ML models (resolves Can't instantiate Geoparser #80)
• retrains the statistical models to account for gazetteer and library changes
• added a step that constrains the lookup to PCLI types if the search term is a country name (resolves USA is getting labeled with a feature code 'BLDG' #77)