Remove the white screen of welcome

If there's no home page configured, view the first room.

src/utils/pages.js

@@ -0,0 +1,31 @@
+/*
+Copyright 2019 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.
+*/
+
+export function getHomePageUrl(appConfig) {
+    const pagesConfig = appConfig.embeddedPages;
+    let pageUrl = null;
+    if (pagesConfig) {
+        pageUrl = pagesConfig.homeUrl;
+    }
+    if (!pageUrl) {
+        // This is a deprecated config option for the home page
+        // (despite the name, given we also now have a welcome
+        // page, which is not the same).
+        pageUrl = appConfig.welcomePageUrl;
+    }
+
+    return pageUrl;
+}