Passing pre-initialized spaCy `nlp` object to `Geoparser` initialization causes error

[ahalterman]

There's an option to load the nlp object first, then pass it to Geoparser when that object gets initialized. However, it doesn't check that the ._.tensor attribute is loaded on the nlp object. Since it's not likely that people would think to do that (including me!) you can get an opaque error.

Either:

• remove option to pass in nlp object
• check if the nlp object has the special tensor attribute registered, and if not, try to add it.