As a user, I want to be able to enter notes for selected nodes and edges.

• If a selected node or edge does not have a note, a new note is created.
• If a note exists already, it can be edited/extended/deleted.
• Notes can be hidden and shown (all at once or only the note of a selected node or edge).
• Notes can be saved and loaded.
• Notes can be either private or public. Private notes are shown to the author only. Public notes are shown to all players. All players can edit/extend/delete all public notes.