[Feature] Better detection for organ/synth parts

## Description

I'm amazed and in love with Spleeter, but one of the problems I keep noticing is the inability for the current models to accurately isolate electronic keyboard sounds, especially organs/synth parts or anything similarly 'droney' like accordions. I wondered whether there might be any scope to improve the detection/isolation of these instruments, or whether they're just sonically too similar to other instruments Spleeter is listening for, like guitars?

## Additional information