Issue Checklist

• I have read the Contributing Guide
• I have checked the Issues/Discussions pages to see if my enhancement has already been suggested
• I have properly titled my enhancement

What is your suggestion, and why should it be implemented?

While you can hide individual songs from Freeplay by returning nothing for listDifficulties(), this becomes an issue when multiple levels include the same song. While the reason to do so is a bit niche, this causes the song to get duplicated in the Freeplay list with the only way to remove the duplicate is by... duplicating the song itself in your mod with a different ID then returning nothing for listDifficulties(). This works but is obviously horrible for the mod's file size.

A potential solution to this is to add a visibleFreeplay variable to the level data schema, where if it's set to false the level is skipped when the Freeplay list is being generated.