Add address settings

[karimone]

Prior to this change to modify the address javascript you had to fork
and edit the address.js manually. This change let to define a setting
dict to customize the address.js.

e.g.

ADDRESS_SETTINGS = {
    'country': ['AU'],
}

it will be injected in the address.js to limit the address to the
australian country.

To achieve that I move the address.js from a static file to a
templateview and threat the address.js file as a django template.

The TemplateView is responsible to retrieve the settings and generate
the context for the template.

There is a requirement to make django-address works now. The url must be
added in your project:

e.g.

urlpatterns = [
    # ... other urls
    path('address/', include('address.urls')),
]

[karimone]

I did some tests and I have a circular import issue, I'll have a look