rename newUnreadMessage to newInteraction

- newUnreadMessage was used only for messages. It will soon be used for
  data transfer.

- WARNING : all lrc clients need to be updated

Change-Id: Ie7b48767b36ea449c2405d796ed6faa6ea02ba51
Reviewed-by: Anthony Léonard <anthony.leonard@savoirfairelinux.com>