* 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
* Remove enableGallery feature flag
* Fix bugs
* Add tests to increase coverage
* Move favorites functionality behind feature.enableGalleryPublish flag
* Show code cells in NotebookViewer
* Use cosmos db logo as persona image for sample notebook gallery cards
* Update gallery card snapshot to fix test
* 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
