Problem with multidisc album with disc subtitle

[paultaylor]

I think the solution to this will be to add a MINIMSERVER_DISCSUBTITLE field which stores disc subtitle if has one, or disc n if does not. Therefore within MinimServer can enable disc grouping for all multidisc albums by replacing DISCSUBTITLE with this field.

Cannot decide whether to make this specifically a MinimServer field or if there is another more generic name I could use.