add screencast

src/assets/i18n/help/help-de.html

 <mat-dialog-content>
 
-  <h2>Rolle Dozent</h2>
-  <p>Screencast in Vorbereitung</p>
+  <h2>Nutzungs-Szenario</h2>
 
-  <!-- TODO
 <div class="video">
   <div class="videoWrapper">
     <iframe tabindex="0"
-            width="560" height="349"
+            width="560" height="315"
             [ngClass]="{'mobileFrame': deviceType === 'mobile', 'desktopFrame': deviceType === 'desktop'}"
-            src="https://www.youtube.com/embed/RODwmMxLKa0?autoplay=0" frameborder="0"
+            src="https://www.youtube.com/embed/0mxQxPmU9Aw?autoplay=0" frameborder="0"
             allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen
     ></iframe>
   </div>
 </div>
--->
-
-  <h2>Rolle Moderator</h2>
-  <p>Screencast in Vorbereitung</p>
-
-  <h2>Rolle Student</h2>
-  <p>Screencast in Vorbereitung</p>
 
 </mat-dialog-content>