FIX: optimize media file panel

1. disable select when no file
2. disable batch edit button when no selection
3. hide batch edit when no file
4. delete/play/open_folder for downloaded file
5. hide type panel

Change-Id: Ida00da366a8f59b2c5028ddcf87e197c20a21e44

src/slic3r/GUI/MediaFilePanel.h

@@ -39,6 +39,8 @@ public:
 public:
     void Rescale();
 
+    void SetSelecting(bool selecting);
+
 private:
     void modeChanged(wxCommandEvent & e);