Notification system enhanced

- Base for notifcation center
- Show text in map if no data is available

frontend/src/app/map/map.component.html

@@ -36,4 +36,8 @@
         position="top-right"
       ></mgl-control>
     </div>
-</mgl-map>
+</mgl-map>
+<div id="noData" *ngIf="!this.showMap">
+  <h1>There is no data</h1><br>
+  <p>Selected time span does not contain any coordiantes.</p>
+</div>