Add note command

Add a note command that adds silently a note to a user's modlog for other auth to read without giving actual punishment and without having the whole chat knowing.
Revamp note command, now modnote

Make it clear that it's a private user. Mod notes are no longer restricted to an user, all mods can add a note for anything.
Merge pull request #251 from Joimer/patch-22

Add note command