added redirector component (#199)

* added redirector component
    * it will redirect every request to /$something that is not handled otherwise (/intro, /login and such) to /n/$something
* added getNote API Call
* added NotFound component
* added LandingLayout around the NotFound component, so users can easily navigate away from the component

Signed-off-by: Philip Molares <philip.molares@udo.edu>

src/api/note.ts

@@ -1,6 +1,29 @@
 import { expectResponseCode, getBackendUrl } from '../utils/apiUtils'
 import { defaultFetchConfig } from './default'
 
+interface LastChange {
+  userId: string
+  username: string
+  timestamp: number
+}
+
+export interface Note {
+  id: string
+  alias: string
+  lastChange: LastChange
+  viewcount: number
+  createtime: string
+  content: string
+  authorship: number[]
+  preVersionTwoNote: boolean
+}
+
+export const getNote = async (noteId: string): Promise<Note> => {
+  const response = await fetch(getBackendUrl() + `/notes/${noteId}`)
+  expectResponseCode(response)
+  return await response.json() as Promise<Note>
+}
+
 export const deleteNote = async (noteId: string): Promise<void> => {
   const response = await fetch(getBackendUrl() + `/notes/${noteId}`, {
     ...defaultFetchConfig,