Beta working implementation of nested notes
* Tested :
  - Creating a note
    - Increments the rank of following notes
    - Spawn under the previous note
  - Tabing a note
    - Sets the previous note with same depth as parent
    - Increase depth of tabbed note, and all it's descendants
    - Sets the right rank in new depth
    - Decrease the rank of previous following notes
  - Delete a note
    - Delete the entire subtree (all descendants)
    - Decrease the rank of following notes