message: Clear error message when focusing any form element
  (identical behavior as on Login screen)
diff: <mat-form-field appearance="outline">
  <mat-label translate>LABEL_EMAIL</mat-label>
  - <input [formControl]="emailControl" type="text" matInput>
  + <input [formControl]="emailControl" (focus)="this.error=null" type="text" matInput>
  <mat-error *ngIf="emailControl.invalid && emailControl.errors.required" translate>MANDATORY_EMAIL</mat-error>
  <mat-error *ngIf="emailControl.invalid && emailControl.errors.email" translate>INVALID_EMAIL</mat-error>
  </mat-form-field>
  <mat-form-field appearance="outline">
  <mat-label translate>LABEL_PASSWORD</mat-label>
  - <input [formControl]="passwordControl" type="password" matInput>
  + <input [formControl]="passwordControl" (focus)="this.error=null" type="password" matInput>
  <mat-error *ngIf="passwordControl.invalid && passwordControl.errors.required" translate>MANDATORY_PASSWORD</mat-error>
  <mat-error
  *ngIf="passwordControl.invalid && (passwordControl.errors.minlength || passwordControl.errors.maxlength)" translate [translateParams]="{length: '5-20'}">INVALID_PASSWORD_LENGTH</mat-error>
  <mat-form-field appearance="outline">
  <mat-label translate>LABEL_PASSWORD_REPEAT</mat-label>
  - <input [formControl]="repeatPasswordControl" type="password" matInput>
  + <input [formControl]="repeatPasswordControl" (focus)="this.error=null" type="password" matInput>
  <mat-error *ngIf="repeatPasswordControl.invalid && repeatPasswordControl.errors.required" translate>MANDATORY_PASSWORD_REPEAT</mat-error>
  </mat-form-field>
  <em style="margin-left:5px;" translate>CANNOT_BE_CHANGED_LATER</em>
  </mat-label>
  <mat-select [formControl]="securityQuestionControl" placeholder="" [(value)]="selected"
  - name="securityQuestion">
  + (focus)="this.error=null" name="securityQuestion">
  <mat-option *ngFor="let question of securityQuestions" [value]="question.id">
  {{question.question}}
  </mat-option>
  </mat-form-field>
  <mat-form-field appearance="outline">
  - <input [formControl]="securityAnswerControl" type="text" matInput [placeholder]="'SECURITY_ANSWER_PLACEHOLDER' | translate">
  + <input [formControl]="securityAnswerControl" (focus)="this.error=null" type="text" matInput [placeholder]="'SECURITY_ANSWER_PLACEHOLDER' | translate">
  <mat-error *ngIf="securityAnswerControl.invalid && securityAnswerControl.errors.required" translate>MANDATORY_SECURITY_ANSWER</mat-error>
  </mat-form-field>
  </div>
  