new commit:

Made a ChecklistItem array to replace the instance variable ChecklistItems. Then created local ChecklistItems objects inside init (coder aDecoder: NSCoder), and appended the objects to the ChecklistItem array.

Need to fix the tableView(didSelectRowAtIndexPath) and configureCheckmarkCell(cell, indexPath)
Made changes to the functions.
Used the ChecklistItem array inside the functions and used the indexPath.row as the index for the array.