Add a blockabstract for subjects
    this is basically a placeholder

    The subject type attribute is used for a few important neverallow rules, and is the basis for all process types

    By not associating any rules other than the fundamental neverallow rules we provide flexibility by providing a way to create subjects
    with almost no rules associated with them. In practice subject_common_type is associated with subjects as this type attribute is
    associated with rules pretty much common to all subjects (give and take) plus the fundamental never allow rules