Improve resume playback on startup, re-request stream URL when unpausing

Fixes #270

src/core/mainwindow.h

@@ -242,7 +242,6 @@ class MainWindow : public QMainWindow, public PlatformInterface {
   void SavePlaybackStatus();
   void LoadPlaybackStatus();
   void ResumePlayback();
-  void ResumePlaybackSeek(const int playback_position);
 
   void Exit();
   void DoExit();