auto-add disc numbers

[tymbalodeon]

albums often come in with disc numbers blank, but I prefer to see disc 1 of 1 instead of null. add an option to fill in blank disc numbers with disc 1 of 1 (more often than not this is accurate for blank disc numbers, but this can be made optional)

[tymbalodeon]

Only do this if [disc *] not present in album title. If [disc *] present in album title, use * for disc number. Can't auto-add disc total because it's possible that only the first few discs would be uploaded as a correction to metadata, but not the rest of the set.