Add user via api

Leave original user object in for this slice. Remove on next

app/notify_client/user_api_client.py

@@ -0,0 +1,18 @@
+from client.notifications import BaseAPIClient
+
+
+class UserApiClient(BaseAPIClient):
+
+    def __init__(self, base_url, client_id, secret):
+        super(self.__class__, self).__init__(base_url=base_url,
+                                             client_id=client_id,
+                                             secret=secret)
+
+    def register_user(self, name, email_address,  mobile_number, password):
+        data = {
+            "name": name,
+            "email_address": email_address,
+            "mobile_number": mobile_number,
+            "password": password}
+
+        return self.post("/user", data)