Adding checklist item drag and drop feature

**I see my commit but didn't know it was going to do all of them. I'll be more cautious on my pull request in the future. Reject if needed.** This commit will allow a user to drag and drop their checklist items. I have decided to not do any changes to the keyboard navigation, adding, and removal, just to be safe. I think it'd make it more annoying to use to change it, so will hold off on that.