Allow linking notes to specific Tasks

[CaAlden]

Notes are valid as top level entries in the bullet journal, but often the pertain only to a single task and should always be carried with that task.

Tasks for resolving this:

• Add notes to entries as an array of note tasks
• Create a UI for attaching notes to a task
  1. Create a new note attached to a task
  2. Attach an existing top level note to a task
• Create a ui for rendering notes as elements below a given task.

[CaAlden]

I'm realizing that "Sub Entries" is sort of the real feature I want. The ability to break up a task into multiple elements with potentially attached notes. It would additionally be nice to create a sort of topology in the sub tasks so you could define some ordering of things that must happen before others.