Basic Pluto-like display functionality outside of Pluto (e.g. VSCode pane, browser)

[disberd]

Discussed yesterday at the Pluto dev meeting with @fonsp, it would be cool to extract some basic functionality of the Pluto webserver and the communication between julia and HTML/JS similar to how it works in Pluto, so that one can use the same function/synthax (both in Julia and JS) even when outside of Pluto.

Ideally it would be nice to have a very lightweight implementation that just has webserver/websocket and support for the new with_js_link from #13.

This would allow packages (e.g. PlutoPlotly) to seamelessly provide advance interactivity with a unique synthax both inside and outside of Pluto.