add feature flag for song notifications

enables users/distributions to ship without dbus dependency

src/queue.rs

@@ -1,7 +1,9 @@
 use std::cmp::Ordering;
 use std::sync::{Arc, RwLock};
 
+#[cfg(feature = "notify")]
 use notify_rust::Notification;
+
 use rand::prelude::*;
 use strum_macros::Display;
 
@@ -221,6 +223,7 @@ impl Queue {
             current.replace(index);
             self.spotify.update_track();
             if self.spotify.cfg.notify.unwrap_or(false) {
+                #[cfg(feature = "notify")]
                 if let Err(e) = Notification::new().summary(&track.to_string()).show() {
                     error!("error showing notification: {:?}", e);
                 }