ConsentResource to gather policy consent from users

Hopefully there are enough comments and docs in this that it makes sense on its
own.

synapse/storage/registration.py

@@ -286,6 +286,24 @@ class RegistrationStore(RegistrationWorkerStore,
             "user_set_password_hash", user_set_password_hash_txn
         )
 
+    def user_set_consent_version(self, user_id, consent_version):
+        """Updates the user table to record privacy policy consent
+
+        Args:
+            user_id (str): full mxid of the user to update
+            consent_version (str): version of the policy the user has consented
+                to
+
+        Raises:
+            StoreError(404) if user not found
+        """
+        return self._simple_update_one(
+            table='users',
+            keyvalues={'name': user_id, },
+            updatevalues={'consent_version': consent_version, },
+            desc="user_set_consent_version"
+        )
+
     def user_delete_access_tokens(self, user_id, except_token_id=None,
                                   device_id=None):
         """

synapse/storage/schema/delta/48/add_user_consent.sql

@@ -0,0 +1,18 @@
+/* Copyright 2018 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* record the version of the privacy policy the user has consented to
+ */
+ALTER TABLE users ADD COLUMN consent_version TEXT;