Watch folder for notebook changes and update automagically

[fonsp]

After scanning a directory for notebook files, you can now ask Pluto to continue watching the directory for changes. When notebook files are added/removed, they are also added/removed from the server. When a notebook file changes, the notebook session is restarted.

This works especially well when this directory is a git-tracked directory. When running in a git directory, PlutoSliderServer can keep git pulling the directory, updating from the repository automatically.

Continuous Deployment

The result is a Continuous Deployment setup: you can set up your PlutoSliderServer on a dedicated server running online, synced with your repository on github. You can then update the repository, and the PlutoSliderServer will update automatically.

The alternative is to redeploy the entire server every time a notebook changes. We found that this setup works fairly well, but causes long downtimes whenever a notebook changes, because all notebooks need to re-run. This can be a problem if your project consists of many notebooks, and they change frequently.

TODO:

• Show progress in logs (e.g. [12/29] ready)
• git reset? Don't delete html files? Require separate output folder?
• Check for concurrency stuff
• Remove the many example config files? Will be easy to forget to update
• Automatic docstrings from Config structs
• Automatic sample toml file
• Include fix settings #30, Fix behavior of run_directory when static_export option is given #28
• Option to update from file using pluto instead of re-running
• Some notebooks should always rerun because they depend on other notebooks
• Docstring for run_git_directory

Continuation of #11