Notebooks Gallery (#59)

* Initial commit

* Address PR comments

* Move notebook related stuff to NotebookManager and dynamically load it

* Add New gallery callout and other UI tweaks

* Update test snapshot

src/Shared/StorageUtility.ts

@@ -71,6 +71,5 @@ export enum StorageKey {
   TenantId,
   MostRecentActivity,
   SetPartitionKeyUndefined,
-  NotebookMetadata,
-  NotebookName
+  GalleryCalloutDismissed
 }