Moved the model meta data for roles and columns into "model/metadata.h" to gather meta data like this in one central place.

model/commands/edititemcommand.h

@@ -8,6 +8,9 @@ class TableModel;
 
 class EditItemCommand : public QUndoCommand {
  public:
+  // TODO don't use simple pointer to model
+  /// Using simple pointer to model because there was a crash when closing the application with an
+  /// unclean undo stack
   EditItemCommand(TableModel* model,
                   const QModelIndex& index,
                   QMap<int, QVariant>& changedValues,