Added support for taking screenshot during Notebook publish to Gallery (#108)

* Added support for taking screenshot

- Screenshot is taken using html2canvas package
- Converted to base 64 and uploaded to metadata
- For Using first display output
  - Notebok object is passed instead of string, to publish pane
  - The first cell with output present is parsed out
  - The dom is also parsed to get corresponding div element to take screenshot of the first output

* fixed bug

* Addressed PR comments

- FIxed bug that didn't capture screenshot when mutiple notebook tabs are opened

* removed unnecessary dependencies

* fixed compile issues

* more edits

src/Explorer/Tabs/NotebookV2Tab.ts

@@ -449,7 +449,11 @@ export default class NotebookTabV2 extends TabsBase implements ViewModels.Tab {
 
   private publishToGallery = () => {
     const notebookContent = this.notebookComponentAdapter.getContent();
-    this.container.publishNotebook(notebookContent.name, notebookContent.content);
+    this.container.publishNotebook(
+      notebookContent.name,
+      notebookContent.content,
+      this.notebookComponentAdapter.getNotebookParentElement()
+    );
   };
 
   private traceTelemetry(actionType: number) {