Fix createNote to return Note instead of Node

[caleb-walz12]

Consider the following:

note = keep.createNote('title', 'text')
note.pinned = True

This shows a warning that 'Node' object has no attribute 'pinned'. The object returned from createNote is actually a Note and has attribute pinned, so no error is raised. However, createNote should indicate that it returns a Note to avoid this warning.