Create tabs manager and refactor tab related logic (#66)

Co-authored-by: Steve Faulkner <southpolesteve@gmail.com>

src/Explorer/SplashScreen/SplashScreenComponentAdapter.test.ts

@@ -1,15 +1,16 @@
 import * as ko from "knockout";
 import { DataSamplesUtil } from "../DataSamples/DataSamplesUtil";
 import { SplashScreenComponentAdapter } from "./SplashScreenComponentApdapter";
+import { TabsManager } from "../Tabs/TabsManager";
 import Explorer from "../Explorer";
 jest.mock("../Explorer");
 
 const createExplorer = () => {
   const mock = new Explorer({} as any);
-  mock.openedTabs = ko.observableArray([]);
   mock.selectedNode = ko.observable();
   mock.isNotebookEnabled = ko.observable(false);
   mock.addCollectionText = ko.observable("add collection");
+  mock.tabsManager = new TabsManager();
   return mock as jest.Mocked<Explorer>;
 };