New feature: Jupyter Books (#6095)

* Initial commit

* Fixed broken branch

* Show notebook titles in tree view

* Added  README

* sections showing in tree view

* Multiple books in treeview

* removed book extension, added to notebook

* removed book from extensions.ts

* addressed Chris' comments

* Addressed Charles' comments

* fixed spelling in readme

* added comment about same filenames

* adding vsix

* addressed Karl's comments

extensions/notebook/src/book/bookTreeItem.ts

@@ -0,0 +1,24 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as vscode from 'vscode';
+
+export class BookTreeItem extends vscode.TreeItem {
+
+	constructor(
+		public readonly title: string,
+		public readonly root: string,
+		public readonly tableOfContents: any[],
+		public readonly collapsibleState: vscode.TreeItemCollapsibleState,
+		public uri?: string,
+		public readonly type?: vscode.FileType,
+		public command?: vscode.Command
+	) {
+		super(title, collapsibleState);
+	}
+
+	contextValue = 'book';
+
+}