Let the upgrade to convert all attachments

Signed-off-by: Suki <suki@missallsunday.com>
Add the ".dat" extension

Signed-off-by: Suki <suki@missallsunday.com>
getLegacyAttachmentFilename() shouldn't be required anymore

Signed-off-by: Suki <suki@missallsunday.com>
redirect moderators to BoardIndex #956

Signed-off-by: Suki <suki@missallsunday.com>
Yet another hook

Signed-off-by: Suki <suki@missallsunday.com>