Added method to count currently playing tracks in Output classes

src/output/output.cpp

@@ -60,6 +60,10 @@ namespace Mist {
     isBlocking = blocking;
     myConn.setBlocking(isBlocking);
   }
+  
+  uint32_t Output::currTrackCount() const{
+    return buffer.size();
+  }
 
   void Output::updateMeta(){
     //read metadata from page to myMeta variable

src/output/output.h

@@ -53,6 +53,7 @@ namespace Mist {
       void selectDefaultTracks();
       bool connectToFile(std::string file);
       static bool listenMode(){return true;}
+      uint32_t currTrackCount() const;
       virtual bool isReadyForPlay();
       //virtuals. The optional virtuals have default implementations that do as little as possible.
       virtual void sendNext() {}//REQUIRED! Others are optional.