[WIP] added endpoint and dao to create invites for users.

Droped token as later code to send email invite can generate
timebased url to send to user. That can then be checked
against configurable time threshold for expiry. Therefore
no need to store a token.

tests/app/dao/test_invited_user_dao.py

@@ -0,0 +1,23 @@
+
+from app.models import InvitedUser
+
+from app.dao.invited_user_dao import save_invited_user
+
+
+def test_create_invited_user(notify_db, notify_db_session, sample_service):
+    assert InvitedUser.query.count() == 0
+    email_address = 'invited_user@service.gov.uk'
+    invite_from = sample_service.users[0]
+
+    data = {
+        'service': sample_service,
+        'email_address': email_address,
+        'from_user': invite_from
+    }
+
+    invited_user = InvitedUser(**data)
+    save_invited_user(invited_user)
+
+    assert InvitedUser.query.count() == 1
+    assert invited_user.email_address == email_address
+    assert invited_user.from_user == invite_from