Add hu berlin requirement (#4500)

* add new requirement

* update demo copyright

* update sf-font

* optimize code

* improve variables naming

frontend/src/components/common/logout.js

@@ -0,0 +1,18 @@
+import React from 'react';
+import { siteRoot, gettext } from '../../utils/constants'
+
+export default function Logout() {
+  const style = {
+    width: '32px',
+    height: '32px',
+    marginLeft: '8px',
+    color: '#bbb',
+    textDecoration: 'none'
+  };
+  const classname = "d-flex align-items-center justify-content-center"
+  return (
+    <a className={classname} style={style} href={`${siteRoot}accounts/logout/`} title={gettext('Logout')}>
+      <i className="sf3-font sf3-font-logout" style={{fontSize: '24px'}}></i>
+    </a>
+  )
+}