addItem Refactor

- Changes `KDListViewController` `@itemOrdered` to be a reflection of its `listView`'s items.
- Removes unnecessary logic from controller for items to be needed.
- Fixes the behavior of the `KDListView`'s item addition.
  - It works for both `boxed` and `!boxed`.
  - It works for both `lastToFirst` and `!lastToFirst`