project: added revert function

This can be triggered either with File > Revert or by re-opening an already open project

Fixes #1710

app/core.h

@@ -329,6 +329,11 @@ public slots:
    */
   bool SaveAllProjects();
 
+  /**
+   * @brief Revert project to last saved state (basically close and open it)
+   */
+  void RevertActiveProject();
+
   /**
    * @brief Closes the active project
    *
@@ -506,6 +511,8 @@ private:
 
   void SaveUnrecoveredList();
 
+  bool RevertProjectInternal(Project *p, bool by_opening_existing);
+
   /**
    * @brief Internal main window object
    */