On day pages, a task created from a note should contain a reference to
the note. However, only one task should be created on that day page.

On plan pages, a task created from a note should contain a reference
to the note. Two tasks will be created – one on the plan page and one
on the day page. The plan page task will refer to the day page while
the day page refers to the plan page. Updating the day page task
should update the plan page task as well. This presents a problem, as
the link text might disappear when we copy or move the task. We should
test this.