Built-in browser local file saving in Chrome

[ctrekker]

File handles for a user's local files can be obtained upon request via the File System Access API. This API is currently only available on Chrome, so as a fallback the current method of file saving will be used instead.

Here's a link to a demo of what I have thus far: https://youtu.be/IyNrHnQETGI

Try it out!

julia> ]
pkg> activate --temp
pkg> add https://github.com/ctrekker/Pluto.jl#browser-local-saving
julia> import Pluto; Pluto.run()

[fonsp]

To repeat what we discussed in the Pluto call:

This is AWESOME, and we will use it for binder soon!

We won't enable it by default for the registered Pluto yet, because we only get the file, not its location. Notebooks that depend on other files and use code like ./data/friends.csv will not work :( Not yet sure how to solve this smoothly