Content-Type for CSV download is imprecise and ambiguous

[Conal-Tuohy]

When I download a CSV file containing a transcription (Expedition admin/Tools/Export all tasks/Single de-normalised CSV file), the server sends an HTTP Content-Type header which declares the content to be plain text, rather than CSV:

content-type: text/plain

The correct media type is text/csv.

Secondly, and more importantly, the content-type header doesn't explicitly declare a character encoding. Note that the IANA media type registration for text/csv recommends that applications should interpret a CSV without an explicitly defined encoding as UTF-8, and it also recommends that an explicit encoding be provided, e.g.

content-type: text/csv; charset=utf-8

Typically this metadata would be lost when a browser saves the CSV to a file, but its existence in the HTTP message would still be a valuable statement to any developers working with CSV files sourced from digivol.