Add feature for "administrative area"

[brylie]

It is often the responsible of some governmental subdivision to make decisions about (sub)urban design. There are many names for the governmental subdivision, depending on the country. Some examples include "municipality", "commune", "local-government area", and "duchy". The phrase "administrative area" seems to be a fairly generic representation of the many types of governmental subdivisions.

Immediate need

We want to be able to document the structure and activities of the Finnish Hinku network, who are responsible for implementing the 2030 agenda of carbon-neutral Finland.

Design

AdminstrativeArea should have the following attributes

• name
• description
• website
• area_type (enum of allowed values)

An AdministrativeArea can contain other AdministrativeAreas. Consider using a tree model, such as django-mptt.

AdministrativeArea can be related (many-to-many or one-to-many?) with Project(s).
AdministrativeArea can be related (many-to-many) with Group(s). #155

[brylie]

Should sustainability goals be associated (also) with administrative areas?