store locale + theme in profile, add theme switch

src/app/app.component.html

@@ -9,13 +9,18 @@
   <span class="spacer"></span>
   <ng-container>
 
-    <button *ngIf="locales.length > 1" mat-button [matMenuTriggerFor]="menu">
-      <mat-icon>language</mat-icon>
+    <button mat-button [matMenuTriggerFor]="menu">
+      <mat-icon>settings</mat-icon>
       <mat-icon>arrow_drop_down</mat-icon>
     </button>
     <mat-menu #menu="matMenu">
       <a *ngFor="let locale of locales" mat-menu-item (click)="setLocale(locale)">{{'locale.' + locale + '.long' |
-        i18n}} <mat-icon  inline=true  *ngIf="locale == currentLocale">done</mat-icon></a>
+        i18n}} <mat-icon inline=true *ngIf="locale == currentLocale">done</mat-icon></a>
+      <a mat-menu-item>
+        <mat-slide-toggle (change)="darkThemeChange($event)" [checked]="darkTheme  == 'true'">
+          {{'profileField.name.darkTheme' | i18n}}
+        </mat-slide-toggle>
+      </a>
     </mat-menu>
   </ng-container>
 </mat-toolbar>