message: show deactivated flag on course card
diff: </button>
  <button mat-icon-button (click)="showReport(course._id)"
  - *ngIf="isCourseTeacherOrAdmin(course)">
  + *ngIf="isCourseTeacherOrAdmin(course) && course.active">
  <mat-icon>show_chart</mat-icon>
  </button>
  + <button mat-icon-button (click)="showReport(course._id)"
  + *ngIf="isCourseTeacherOrAdmin(course) && !course.active" disabled>
  + <mat-icon color="warn">visibility_off</mat-icon>
  + </button>
  +
  <button mat-mini-fab *ngIf="isCourseTeacherOrAdmin(course) || isMemberOfCourse(course)"
  color="primary" class="details-button" [routerLink]="['course', course._id]">
  <mat-icon>arrow_forward</mat-icon>
  