Created a setting for the default value for approval prompt.

The approval prompt could be set via a settings file for a project rather than having to create a view which inherits from the AuthorizationView and overrides the get method.

    def get(self, request, *args, **kwargs):
        req = request.GET.copy()
        req.setdefault('approval_prompt', 'auto')
        request.GET = req
        return super(AuthorizeView, self).get(request, *args, **kwargs)