Simplify example geocoding notebook

[kbrose]

Right now the geocoding example notebook uses the NER dataset from kaggle. Current best results are achieved using only our own training data downloadable from https://geo-extract-tester.herokuapp.com. To make things as easy as possible, the example notebook should be updated to download our training.txt file and not kaggle's.

Notebook in question: https://github.com/chicago-justice-project/article-tagging/blob/master/lib/notebooks/extract-geostring-example.ipynb