Added a confirmation Dialog when trying to close a tab

src/widgets/notebook.hpp

@@ -6,6 +6,7 @@
 #include "widgets/splitcontainer.hpp"
 
 #include <QList>
+#include <QMessageBox>
 #include <QWidget>
 
 namespace chatterino {
@@ -73,6 +74,8 @@ private:
 
     void loadTabs();
 
+    QMessageBox closeConfirmDialog;
+
 public:
     void save();
 };