Migrate app to TypeScript (#1637)

* Initial setup and migrated src/common

* WIP

* WIP

* WIP

* Main module basically finished

* Renderer process migrated

* Added CI step and some fixes

* Fixed remainder of issues and added proper ESLint config

* Fixed a couple issues

* Progress!

* Some more fixes

* Fixed a test

* Fix build step

* PR feedback

src/renderer/components/urlDescription.tsx

@@ -0,0 +1,16 @@
+// Copyright (c) 2016-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+import React from 'react';
+
+export default function UrlDescription(props: {url: string}) {
+    if (props.url) {
+        return (
+            <div className='HoveringURL HoveringURL-left'>
+                <p>{props.url}</p>
+            </div>
+        );
+    }
+
+    return null;
+}