Implement updating devices

You can update the displayname of devices now.

synapse/handlers/device.py

@@ -141,6 +141,30 @@ class DeviceHandler(BaseHandler):
         yield self.store.user_delete_access_tokens(user_id,
                                                    device_id=device_id)
 
+    @defer.inlineCallbacks
+    def update_device(self, user_id, device_id, content):
+        """ Update the given device
+
+        Args:
+            user_id (str):
+            device_id (str):
+            content (dict): body of update request
+
+        Returns:
+            defer.Deferred:
+        """
+
+        try:
+            yield self.store.update_device(
+                user_id,
+                device_id,
+                new_display_name=content.get("display_name")
+            )
+        except errors.StoreError, e:
+            if e.code == 404:
+                raise errors.NotFoundError()
+            else:
+                raise
 
 
 def _update_device_from_client_ips(device, client_ips):