Add update check

Closes #338

client/src/components/ui/Update.css

@@ -0,0 +1,6 @@
+.update {
+    position: relative;
+    z-index: 102;
+    margin-bottom: 0;
+    padding: 0.75rem 0;
+}

client/src/components/ui/Update.js

@@ -0,0 +1,19 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+
+import './Update.css';
+
+const Update = props => (
+    <div className="alert alert-info update">
+        <div className="container">
+            {props.announcement} <a href={props.announcementUrl} target="_blank" rel="noopener noreferrer">Click here</a> for more info.
+        </div>
+    </div>
+);
+
+Update.propTypes = {
+    announcement: PropTypes.string.isRequired,
+    announcementUrl: PropTypes.string.isRequired,
+};
+
+export default Update;