Get info about organisations from database table

This is the first step of replacing the `domains.yml` file.

In order to replicate the same functionality we get from the
`domains.yml` file and its associated code this commit adds a
`Organisation` model. This model copies a lot of methods from the
`AgreementInfo` class which wrapped the `domains.yml` file.

It factors out some stuff that would otherwise be duplicated between the
`Organisation` and `Service` model, in such a way that could be reused
for making other models in the future.

This commit doesn’t change other parts of the code to make use of this
new model yet – that will come in subsequent commits.

app/models/user.py

@@ -2,7 +2,10 @@ from itertools import chain
 
 from flask import abort, request, session
 from flask_login import AnonymousUserMixin, UserMixin
+from werkzeug.utils import cached_property
 
+from app.models.organisation import Organisation
+from app.notify_client.organisations_api_client import organisations_client
 from app.utils import is_gov_user
 
 roles = {
@@ -192,6 +195,16 @@ class User(UserMixin):
     def is_locked(self):
         return self.failed_login_count >= self.max_failed_login_count
 
+    @property
+    def email_domain(self):
+        return self.email_address.split('@')[-1]
+
+    @cached_property
+    def default_organisation(self):
+        return Organisation(
+            organisations_client.get_organisation_by_domain(self.email_domain)
+        )
+
     def serialize(self):
         dct = {
             "id": self.id,
@@ -322,3 +335,7 @@ class AnonymousUser(AnonymousUserMixin):
     # set the anonymous user so that if a new browser hits us we don't error http://stackoverflow.com/a/19275188
     def logged_in_elsewhere(self):
         return False
+
+    @property
+    def default_organisation(self):
+        return Organisation(None)