Encoding in downloaded CSV file

[nfee006]

Related to #34. This issue did not appear when I ran the app on my VM/accessed it within a linux environment. I noticed it when I updated main on @ data and accessed the page from my Windows environment.

The "Download summary data as CSV" button created a CSV with encoding issues in french, for example:

It's not consistent though - the encoding is fine (UTF-8) in notepad ++. It's probably just a matter of specifying the encoding when exporting the csv.

Also, the column titles should be changed in the "Download ionograms" CSV as well. They should be the same with the addition of file_path = File path = Chemin de fichier

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