Add button to purge rooms to room list (#44)

* Add button to purge rooms to room list

Add button (BulkDeleteButton) to delete rooms with no local users:
- purge rooms `POST /_synapse/admin/v1/purge_room`
(https://github.com/matrix-org/synapse/blob/master/docs/admin_api/purge_room.md)

* Bugfix of merge 'master'

* Change from purge room to delete room endpoint

src/components/rooms.js

@@ -1,4 +1,4 @@
-import React from "react";
+import React, { Fragment } from "react";
 import { connect } from "react-redux";
 import {
   BooleanField,

src/synapse/dataProvider.js

@@ -66,6 +66,11 @@ const resourceMap = {
     total: json => {
       return json.total_rooms;
     },
+    delete: id => ({
+      endpoint: `/_synapse/admin/v1/rooms/${id}/delete`,
+      body: { block: false },
+      method: "POST",
+    }),
   },
   devices: {
     map: d => ({