Add metadata support for DSF.

[dutchcomputerkid]

DSF files (Extracted SACD music) support ID.3 tags but Subsonic refuses to write to them as it says "Failed to update tags for file Adiemus. No Writer associated with this extension:dsf"

I'm suspecting adding the DSF file format to this Writer applet would probably do the trick? Would be better to not have to browse to the files and grab mp3tag when something needs to be changed.