Alternative search musiclibrary

This PR is NOT meant for pull consideration. It is only made as a basis for discussion for pull request #246.
Yeah this is one of those "walk through the batch and assemble list" patterns.  It's in other code too, in the snapshotting.  I suggested this should be an internal helper on that PR before it was merged.  Maybe this is special because it's got knowledge of the types.

Also about the types, does this code skip the weird stuff you get back from searches - AllArtists, if that's the name.  I tried to get that filter by type but ended up with hacky code like `if item.item_class == 'object.container.album.musicAlbum':`