move individual bundled comics-related af plugins to af_comics

plugins/af_buni/init.php

plugins/af_buttersafe/init.php

plugins/af_comics/init.php

plugins/af_csection/init.php

plugins/af_dilbert/init.php

plugins/af_explosm/init.php

plugins/af_gocomics/init.php

plugins/af_pennyarcade/init.php

plugins/af_threewordphrase/init.php

plugins/af_whomp/init.php