Bug 33635: Add BOM to report exports as CSV

Bug 33635: Add BOM to report exports as CSV

When you export a report as CSV excel will not recognise that it's
encoding is utf-8 unless there is a correct Byte Order Mark prepended to
the file.

This patch adds such a BOM to the output file allowing Excel to treat
the file correctly.

Signed-off-by: Michaela Sieber <michaela.sieber@kit.edu>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>