Adds an info banner to the app (#190)

* added info-banner component to show the banner.text, we got from the backend config. This banner is shown on top of the landing page (intro, history, login/signup and profile) and also on top of the editor and links to `/n/banner`
* added banner to backendConfig Redux state
* added BannerState to the ApplicationState with that the showing of the banner is globally controlled, the banner text is given to the banner component and the timestamp to acknowledge a banner was read by the user
* the timestamp of a dismissed note is saved in the browsers localStorage to determine in the future if the banner should be shown

Signed-off-by: Philip Molares <philip.molares@udo.edu>
Co-authored-by: Erik Michelson <github@erik.michelson.eu>

src/components/landing/layout/info-banner.tsx

@@ -0,0 +1,34 @@
+import React from 'react'
+import { useSelector } from 'react-redux'
+import { Link } from 'react-router-dom'
+import { ApplicationState } from '../../../redux'
+import { Alert, Button } from 'react-bootstrap'
+import { setBanner } from '../../../redux/banner/methods'
+import { ForkAwesomeIcon } from '../../common/fork-awesome/fork-awesome-icon'
+import { ShowIf } from '../../common/show-if/show-if'
+
+export const InfoBanner: React.FC = () => {
+  const bannerState = useSelector((state: ApplicationState) => state.banner)
+
+  const dismissBanner = () => {
+    setBanner({ ...bannerState, show: false })
+    window.localStorage.setItem('bannerTimeStamp', bannerState.timestamp)
+  }
+
+  return (
+    <ShowIf condition={bannerState.show}>
+      <Alert variant='primary' dir='auto' className='mb-0 text-center d-flex flex-row justify-content-center'>
+        <Link to='/s/banner' className='flex-grow-1 align-self-center'>
+          {bannerState.text}
+        </Link>
+        <Button
+          variant='outline-primary'
+          size='sm'
+          className='mx-2'
+          onClick={dismissBanner}>
+          <ForkAwesomeIcon icon='times'/>
+        </Button>
+      </Alert>
+    </ShowIf>
+  )
+}