Added flags for language change

src/app/app.html

@@ -0,0 +1,36 @@
+<mat-toolbar color="primary">
+  <span>{{ 'APP.TITLE' | translate }}</span>
+  <span class="spacer"></span>
+
+  <!-- Language -->
+  <mat-form-field appearance="outline" style="width: 170px; margin-right: 8px;">
+    <mat-select [value]="lang.lang()" (selectionChange)="lang.use($event.value)">
+      <mat-select-trigger>
+        <img class="flag-icon" [src]="lang.lang() === 'de' ? '/assets/flags/de.svg' : '/assets/flags/gb.svg'"
+             alt="" aria-hidden="true">
+        <span style="margin-left: 8px;">
+        {{ lang.lang() === 'de' ? ('LANG.DE' | translate) : ('LANG.EN' | translate) }}
+      </span>
+      </mat-select-trigger>
+
+      <mat-option value="de">
+        <img class="flag-icon" src="/assets/flags/de.svg" alt="" aria-hidden="true">
+        <span> {{ 'LANG.DE' | translate }} </span>
+      </mat-option>
+
+      <mat-option value="en">
+        <img class="flag-icon" src="/assets/flags/gb.svg" alt="" aria-hidden="true">
+        <span> {{ 'LANG.EN' | translate }} </span>
+      </mat-option>
+    </mat-select>
+  </mat-form-field>
+
+  <!-- Theme -->
+  <button mat-icon-button (click)="theme.toggle()">
+    <mat-icon>{{ themeIcon() }}</mat-icon>
+  </button>
+</mat-toolbar>
+
+<main class="container app-surface">
+  <router-outlet />
+</main>