WCMS-41 Added activity_log model for tracking changes on profiles.

 Also added timestamps to department, group, service, person models.
There could be some methods to make creating these a bit easier such as

    def set_acting_user=(user)
      self.acting_user = user.name
      self.acting_user_email = user.email
    end

    def associated=(parent)
      self.associated_id = parent.id
      self.parent = parent.class.to_s
    end