Feature suggestion: support data sets named with UTF8 characters

[nbehrnd]

Running WebPlotDigitizer on GitHub's suggested address, i.e., https://automeris.io/WebPlotDigitizer/, with Firefox 78.4.0 esr in Linux Debian 10, I noticed the name definition of data series apparently does not fully support names including characters outside the English alphabet.

As an example (test data in the .zip archive below) I named the upper green colored slope of your test illustration by its German equivalence, «grün». Aiming for the export of the .csv I see the character ü being substituted by underscore _ in the digitizer's display, and equally when the file saved and written, e.g., to the desktop. For me, this is both surprising and not expected.

It is not mission critical for me, yet would be nice if the scope of characters allowed could be extended. On a keyboard set to the layout «US-international», I obtain most of these characters needed by a combination of keys; i.e., obtain ü by the chord of of the two strokes " + u, for example. This is not only about ä, ö, ü about, but includes é, è, â, ç (not exhaustive list) for French, too.

utf8_characters.zip