automatic locations

Creates a command that generates locations object for locations with many entries. 
Does this with 6 models:
*EntryWeb takes an entry and finds entries with close coordinates
*NetworkCenter evaluates a web of entries and finds the ones that are central
  - --- it's helped by a NestedHashConverter which converts hashes of objects into hashes of coordinates
*DataParser takes a text file with the name of every city, it cleans it, and makes it into a list of city names and coordinates.
*LocationMaker users the NetworkCenter to find coordinates in the center of entry density.  It uses CityNameSearcher to find the names of cities near those coordinates.  Then it generates Location objects for those cities.
Unused block argument - `key`. If it's necessary, use `_` or `_key` as an argument name to indicate that it won't be used.