Add a room view

Change-Id: I20056d997e7a94fd10d03e7d1a8051030ecf7ca4

src/components/rooms.js

@@ -0,0 +1,13 @@
+import React from "react";
+import { Datagrid, List, TextField } from "react-admin";
+
+export const RoomList = props => (
+  <List {...props}>
+    <Datagrid>
+      <TextField source="room_id" />
+      <TextField source="name" />
+      <TextField source="canonical_alias" />
+      <TextField source="joined_members" />
+    </Datagrid>
+  </List>
+);