Add simple alert-confirm for delete user

static/src/app/users/user-list/user-list.component.ts

@@ -62,11 +62,12 @@ export class UserListComponent implements OnInit {
   }
 
   deleteUser(user: User) {
+    if (confirm('Soll der Teilnehmer ' + user.username + ' wirklich gelöscht werden?')) {
       this.userService.deleteUser(user)
         .subscribe((res) => {
-
         })
     }
+  }
 
   filterUsersByFraction(query = '', fractionFilter) {
     this.users$ = this.userService.findUsers(query, fractionFilter);