Split models to prevent circular imports

This commit is the first step to disentangling the models from the API
clients. With the models in the same folder as the API clients it makes
it hard to import the API clients within the model without getting a
circular import.

After this commit the user API clients still has this problem, but at
least the service API client doesn’t.

app/__init__.py

@@ -41,7 +41,8 @@ from werkzeug.local import LocalProxy
 from app import proxy_fix
 from app.config import configs
 from app.asset_fingerprinter import asset_fingerprinter
-from app.notify_client.models import Service
+from app.models.service import Service
+from app.models.user import AnonymousUser
 from app.navigation import (
     CaseworkNavigation,
     HeaderNavigation,
@@ -59,7 +60,6 @@ from app.notify_client.user_api_client import user_api_client
 from app.notify_client.events_api_client import events_api_client
 from app.notify_client.provider_client import provider_client
 from app.notify_client.email_branding_client import email_branding_client
-from app.notify_client.models import AnonymousUser
 from app.notify_client.organisations_api_client import organisations_client
 from app.notify_client.org_invite_api_client import org_invite_api_client
 from app.notify_client.letter_jobs_client import letter_jobs_client