Exercise

1. Put the due date in a label on the table view cells under the text
of the to-do item.

2. Sort the to-do items list based on the due date. This is similar to
what we did with the list of Checklists except that now you're sorting
ChecklistItem objects and you'll be comparing NSDate objects instead of
NSStrings. (NSDate does not have a localizedStandardCompare method but
it does have a regular Compare.