add command/binding to jump to currently playing track

fixes #181

src/queue.rs

@@ -83,12 +83,16 @@ impl Queue {
     }
 
     pub fn get_current(&self) -> Option<Track> {
-        match *self.current_track.read().unwrap() {
+        match self.get_current_index() {
             Some(index) => Some(self.queue.read().unwrap()[index].clone()),
             None => None,
         }
     }
 
+    pub fn get_current_index(&self) -> Option<usize> {
+        *self.current_track.read().unwrap()
+    }
+
     pub fn append(&self, track: &Track) {
         let mut random_order = self.random_order.write().unwrap();
         if let Some(order) = random_order.as_mut() {