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>

public/api/v2/config

@@ -13,6 +13,10 @@
     "email": true,
     "openid": true
   },
+  "banner": {
+      "text": "This is the test banner text",
+      "timestamp": "2020-05-22T20:46:08.962Z"
+  },
   "customAuthNames": {
     "ldap": "FooBar",
     "oauth2": "Olaf2",

public/api/v2/notes/banner

@@ -0,0 +1,14 @@
+{
+    "id": "ABC123",
+    "alias": "banner",
+    "lastChange": {
+        "userId": "snskxnksnxksnxksnx",
+        "username": "testy",
+        "timestamp": 123456789
+    },
+    "viewcount": 0,
+    "createtime": "2020-05-22T20:46:08.962Z",
+    "content": "This is the test banner text",
+    "authorship": [],
+    "preVersionTwoNote": true
+}

public/api/v2/notes/old

@@ -10,5 +10,5 @@
     "createtime": "2020-05-22T20:46:08.962Z",
     "content": "test123",
     "authorship": [],
-    "preVersionTwoNote": true
+    "preVersionTwoNote": false
 }