Code improvements (#1086)

* Extract code into hook
* Refactor code to remove let
* Reformat code
* Extract version-info-modal into components
* Use main block in landinglayout
* Add fixedWidth and classname attribute to IconButton

Signed-off-by: Tilman Vatteroth <tilman.vatteroth@tu-dortmund.de>

src/components/landing-layout/footer/version-info/version-info-link.tsx

@@ -0,0 +1,25 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import React, { Fragment, useCallback, useState } from 'react'
+import { Trans } from 'react-i18next'
+import { Link } from 'react-router-dom'
+import { VersionInfoModal } from './version-info-modal'
+
+export const VersionInfoLink: React.FC = () => {
+  const [show, setShow] = useState(false)
+  const closeModal = useCallback(() => setShow(false), [])
+  const showModal = useCallback(() => setShow(true), [])
+
+  return (
+    <Fragment>
+      <Link data-cy={ 'show-version-modal' } to={ '#' } className={ 'text-light' } onClick={ showModal }>
+        <Trans i18nKey={ 'landing.versionInfo.versionInfo' }/>
+      </Link>
+      <VersionInfoModal onHide={ closeModal } show={ show }/>
+    </Fragment>
+  )
+}