Added nav-bar to show home link and user status

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

@@ -0,0 +1,5 @@
+.fill-remaining-space {
+  /* This fills the remaining space, by using flexbox.
+     Every toolbar row uses a flexbox row layout. */
+  flex: 1 1 auto;
+}

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>

bookie/src/app/nav-bar/nav-bar.component.spec.ts

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+import { async, ComponentFixture, TestBed } from '@angular/core/testing';
+
+import { NavBarComponent } from './nav-bar.component';
+
+describe('NavBarComponent', () => {
+  let component: NavBarComponent;
+  let fixture: ComponentFixture<NavBarComponent>;
+
+  beforeEach(async(() => {
+    TestBed.configureTestingModule({
+      declarations: [ NavBarComponent ]
+    })
+    .compileComponents();
+  }));
+
+  beforeEach(() => {
+    fixture = TestBed.createComponent(NavBarComponent);
+    component = fixture.componentInstance;
+    fixture.detectChanges();
+  });
+
+  it('should create', () => {
+    expect(component).toBeTruthy();
+  });
+});

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

@@ -0,0 +1,24 @@
+import { Component, OnInit } from '@angular/core';
+import { Observable } from "rxjs";
+import { map, share } from "rxjs/operators";
+import { AuthService } from "../auth/auth.service";
+
+@Component({
+  selector: 'app-nav-bar',
+  templateUrl: './nav-bar.component.html',
+  styleUrls: ['./nav-bar.component.css']
+})
+export class NavBarComponent implements OnInit {
+  public user: Observable<string>;
+
+  constructor(public auth: AuthService) {
+  }
+
+  ngOnInit() {
+    this.user = this.auth.userObservable.pipe(
+      map (x => x.isAuthenticated ? x.name : null),
+      share()
+    );
+  }
+
+}