Audio mode for each playlist entry (#909)

- Playlist entries get a second select slide for the audio mode (normal, instrumental, vocals, karaoke)
- The slide is only shown if the song has an instrumental file, otherwise normal is used
- The audio mode is saved in the playlist file and used for each round
- Sing, score and highscore screens use the audio mode of the current round
- Song options select the audio mode by mode instead of position
- ScreenSong theme version 15

Co-authored-by: Florian Ostertag <flokuep@users.noreply.github.com>

Output/Themes/Changelog/Changelog_ScreenSong.txt

@@ -1,5 +1,15 @@
 ScreenSong
 
+++++++++++
+Version 15:
+(2026 Oct 16)
+
+Add:
+<SelectSlideAudioMode> in <Playlist> (audio mode for each playlist entry, only shown if the song has an instrumental file)
+
+Change:
+<EntryHeight> of <Playlist> to make room for the second select slide
+
 ++++++++++
 Version 14:
 Add InstrumentalIcon