Insert frame for the English language selection in the footer

frame switches now to the currently selected language box

[Ticket: #129]

src/app/components/shared/footer/footer.component.html

@@ -98,10 +98,14 @@
     <mat-menu #langMenu="matMenu"
               [overlapTrigger]="false">
       <button (click)="useLanguage('de')"
-              class="focus_item"
+              [ngClass]="{
+              'focus_item':getLanguage()==='de',
+              'unfocus_item':getLanguage()!=='de'}"
               mat-menu-item>{{ 'footer.german' | translate }}</button>
       <button (click)="useLanguage('en')"
-              class="focus_item"
+              [ngClass]="{
+              'focus_item':getLanguage()==='en',
+              'unfocus_item':getLanguage()!=='en'}"
               mat-menu-item>{{ 'footer.english' | translate }}</button>
     </mat-menu>
 

src/app/components/shared/footer/footer.component.scss

@@ -206,6 +206,10 @@ mat-icon {
   color: var(--background);
 }
 
-.focus_item:focus {
+.focus_item {
   border: 1px solid var(--on-surface);
 }
+
+.unfocus_item {
+  border: none;
+}