Choose a specific music folder

[jooola]

This is a enhancement but I also faced an issue related to this.

• I have 2 different music folders, and some albums are present in both and are duplicate.
• In the back-end I allow my user only to access the music folder 1.
• In the Airsonic-ui, I can list songs from both music folder.
• After clicking on a track, it plays.
• but after clicking on the duplicate song (not allowed from 2 music folder), I get a 403 (which is expected).

So first I think they are a problem in the back-end that don't separate the music folders right (cc @muff1nman ).
And we need to add the ability to choose between the music folders, and not merge albums if they are duplicate since they are from different music folders.