* Extend LiveMarkdown format to support Elixir snippets in Markdown cells
* Highlight Markdown code blocks using Monaco editor API
* Use livebook metadata for forcing markdown as well
* Keep track of connected clients in session data
* Add API for confirming and purging deltas
* Send delta confirmation from clients once received
* Update naming
* Fix and extend Data tests
* Update naming
* Set up markdown rendering, update theme.
* Improve focus and handle expanding for markdown cells
* Add keybindings for expanding/navigating cells
* Improve editor autofocus when navigating with shortcuts
* Add tests
* Render markdown on the client
* Don't render cell initial data and make a request instead
