Update django address-export manage command to generate a GeoJSON version

[quadrismegistus]

• This would update As a content admin, I want to export member addresses with more details in a separate file so I can more easily work with member locations. #790 to include a representation of the data in GeoJSON form.
• Notes, things to think about/determine:
  • How should the json/data be internally structured? A single record per unique address, containing a list of people who ever lived there; or multiple records with same address/point so there is overlap.