Fix link to content view

src/app/content-list/content-list.component.html

 <mat-list>
   <mat-list-item *ngFor="let content of contents">
-    <button mat-button routerLink="{{content.contentId}}">
+    <button mat-button routerLink="content/{{content.contentId}}">
       Content {{content.contentId}}: {{content.subject}}
     </button>
   </mat-list-item>