[NEW] Add gantt items duplication within same tracker

• Use ganttId to indicate the value to filter items;
• User ganttIdField to indicate the field perm_name that holds the value above;
• Use canDuplicate to indicate if it can duplicate or not (both ganttId and ganttIdField need to have values)
• When duplicating items, a new ganttId is chosen and also the option to update the existing wikiplugin_ganttchart to display the new duplicated items.
• If user does not have permissions to create new tracker items, the duplication is not available.