Go back to basics (simple list of items)
Mark an item as done
Allow new items to be created
Allow items to be edited in-place
Add back 'date' for items and group by that
Use moment.js to format dates; remove GroupableMixin with a custom solution
Add 'day' as a parent of an 'item', instead of items having a 'date' property
Allow items to be added, and sort them alphabetically