Add data model for administrative units and associations reflecting their responsibilities and hierarchy

* Addding a data model for administrative units (See ARCHITECTURE.md for an explanation what exactly those are)
* Adding StateAssociations and SubAssociations to represent the organizational units of DIE LINKE
* Adding a script extracting states, counties, quarters (Bremen), districts (Hamburg, Berlin) and communes (Rhein-Neckar-Kreis) to reflect all administrative units from the OSM Place table
* Adding a script being used for one-time import associations and their relationship to the administrative units
* Adding the resulting data as a fixture.json that can be imported in dev environments or our staging/production system as bootstrapping data

The import scripts are generally not inteded to be reused, as the data is now imported and sanitized in the associations.json fixture. From here on this data is supposed to be managed on the admin interface of django.

refs CAC_SERVICE-4