CAN Inform add handler

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• CAN's inform-add handler should listen to NOTE_EXISTENCE
  • CAN's inform-add handler should inform the user of the existence of the add command when the NOTE_EXISTENCE event is fired and the address field matches the current scratchfile address.
• Can should inform the user of the add command when a new note is in the scratchfile
  • CAN's inform-add handler should listen to NOTE_EXISTENCE, informing the user of the add command. The add command should exist at this point and should fire a COMMAND_ADD event with the user-passed name.