message: refactor card actions
diff: {{course.description}}
  </p>
  </mat-card-content>
  - <mat-card-actions>
  - <button mat-icon-button *ngIf="this.userService.isStudent() && !this.isMemberOfCourse(course)"
  + <mat-card-actions *ngIf="this.userService.isStudent()">
  + <button mat-icon-button *ngIf="!this.isMemberOfCourse(course)"
  (click)="enroll()" matTooltip="Enroll">
  <mat-icon>add_circle_outline</mat-icon>
  </button>
  - <button mat-icon-button *ngIf="this.userService.isStudent() && this.isMemberOfCourse(course)"
  + <button mat-icon-button *ngIf="this.isMemberOfCourse(course)"
  (click)="leave()" matTooltip="Leave">
  <mat-icon>remove_circle_outline</mat-icon>
  </button>
  -
  - <button mat-icon-button (click)="editCourse(course._id)"
  - *ngIf="isCourseTeacherOrAdmin(course)">
  + </mat-card-actions>
  + <mat-card-actions *ngIf="isCourseTeacherOrAdmin(course)">
  + <button mat-icon-button (click)="editCourse(course._id)">
  <mat-icon>mode_edit</mat-icon>
  </button>
  - <button mat-icon-button (click)="showReport(course._id)"
  - *ngIf="isCourseTeacherOrAdmin(course)">
  + <button mat-icon-button (click)="showReport(course._id)">
  <mat-icon>show_chart</mat-icon>
  </button>
  <button mat-icon-button (click)="showReport(course._id)"
  - *ngIf="isCourseTeacherOrAdmin(course) && !course.active" disabled>
  + *ngIf="!course.active" disabled>
  <mat-icon color="warn">visibility_off</mat-icon>
  </button>
  