Make download of files compatible with Safari

[heberleh]

The app uses an outdated library to export files.

It may not work in Safari.

The function saveAs() comes from the old library https://github.com/eligrey/FileSaver.js (npm install file-saver --save)
that can be updated in the code or replaced with a better one.

Here is an example of its use:

saveAs(new Blob([dataset], {type: "text/plain;charset=" + document.characterSet}), document_name);