Added nav-bar to show home link and user status

bookie/src/app/nav-bar/nav-bar.component.html

@@ -0,0 +1,15 @@
+<mat-toolbar>
+  <a mat-button [routerLink]="['/']">
+    <mat-icon>home</mat-icon>
+    Point of Sale
+  </a>
+  <span class="fill-remaining-space"></span>
+  <button mat-button [routerLink]="['/', 'login']" *ngIf="!(user | async)">
+      <mat-icon>account_box</mat-icon>
+      Login
+  </button>
+  <button mat-button [routerLink]="['/', 'logout']" *ngIf="user | async as name">
+      <mat-icon>account_box</mat-icon>
+      Logout {{name}}
+  </button>
+</mat-toolbar>