permission plugin: Output the extratargetfilter virtual attribute
    
    The --filter, --type, and --memberof options interact in a way that's
    difficult to recreate in the UI: type and memberof are "views" on the
    filter, they affect it and are affected by it
    
    Add a "extratagretfilter" view that only contains the filters
    not linked to type or memberof.
    
    Show extra target filter, and not the full target filter, by default;
    show both with --all, and full filter only with --raw.
    
    Write support will be added in a subsequent patch.
    
    Part of the work for: https://fedorahosted.org/freeipa/ticket/4216
    
    Reviewed-By: Martin Kosek <mkosek@redhat.com>