Add duplicate shortcut for events

include/core/event.h

@@ -27,6 +27,7 @@ class Event
 {
 public:
     Event();
+    Event(const Event&);
     Event(QJsonObject, QString);
 public:
     int x() {

include/editor.h

@@ -100,6 +100,7 @@ public:
     Event* createNewEvent(QString event_type);
     void deleteEvent(Event *);
     void updateSelectedEvents();
+    void duplicateSelectedEvents();
     void redrawObject(DraggablePixmapItem *item);
     QList<DraggablePixmapItem *> *getObjects();
 

include/mainwindow.h

@@ -123,6 +123,7 @@ private slots:
 
     void undo();
     void redo();
+    void duplicate();
 
     void openInTextEditor();