Flesh out email templating

Mostly WIP porting the room name calculation logic from the web client so our room names in the email mirror the clients.

synapse/push/emailpusher.py

@@ -82,6 +82,13 @@ class EmailPusher(object):
         self.max_stream_ordering = max(max_stream_ordering, self.max_stream_ordering)
         yield self._process()
 
+    @defer.inlineCallbacks
+    def on_new_receipts(self, min_stream_id, max_stream_id):
+        # We could wake up and cancel the timer but there tend to be quite a
+        # lot of read receipts so it's probably less work to just let the
+        # timer fire
+        return defer.succeed(None)
+
     @defer.inlineCallbacks
     def on_timer(self):
         self.timed_call = None