Embeddable Notebook Update

**Current Status:**

* [x] Users can visit a page and start hack right away
* [x] Any time you make a change and try to close without saving, a warning blocks you
* [x] A button specifically for saving
* [x] Removed old authentication banner
* [x] Removed old save failed link (you now have a dedicated button)
* [x] Finalised style changes
* [x] Popup the modal before authentication
* [x] Remove comment shortcut
* [x] Updated tests
* [x] URL frame persistence

Closes tasks #81, #93, #76, #66, #100, #65, #63, #91, #102, #109