New Livebook default save directory should be the same as the server root

[DaniruKun]

For example, when using an open-command, and a directory is passed (e.g. ~/foo/bar), and I save a new notebook as a file,
the save dialog should be opened at the same directory used in the open command (~/foo/bar), not the home directory.

I think this is more user friendly, as basically any other editor will default to the current directory/workspace location for new files.

[josevalim]

So what you most likely want is to specify the LIVEBOOK_HOME env var when starting it. :) We cannot change the LIVEBOOK_HOME on the script run because otherwise a later run would override an earlier run.