feat: add keyboard shortcuts (#1191)

- implement keyboard shortcuts
- designed user interface to view them

Fixes: #257

src/app/shared/keyboard-shortcuts-dialog/keyboard-shortcuts-dialog.component.spec.ts

@@ -0,0 +1,25 @@
+import { async, ComponentFixture, TestBed } from '@angular/core/testing';
+
+import { KeyboardShortcutsDialogComponent } from './keyboard-shortcuts-dialog.component';
+
+describe('KeyboardShortcutsDialogComponent', () => {
+  let component: KeyboardShortcutsDialogComponent;
+  let fixture: ComponentFixture<KeyboardShortcutsDialogComponent>;
+
+  beforeEach(async(() => {
+    TestBed.configureTestingModule({
+      declarations: [ KeyboardShortcutsDialogComponent ]
+    })
+    .compileComponents();
+  }));
+
+  beforeEach(() => {
+    fixture = TestBed.createComponent(KeyboardShortcutsDialogComponent);
+    component = fixture.componentInstance;
+    fixture.detectChanges();
+  });
+
+  it('should create', () => {
+    expect(component).toBeTruthy();
+  });
+});