Slovak language update

inc/lang/sl/admin.txt

inc/lang/sl/adminplugins.txt

inc/lang/sl/draft.txt

inc/lang/sl/lang.php

inc/lang/sl/subscr_digest.txt

inc/lang/sl/subscr_form.txt

inc/lang/sl/subscr_list.txt

inc/lang/sl/updateprofile.txt

inc/lang/sl/uploadmail.txt

lib/plugins/acl/lang/sl/lang.php

lib/plugins/config/lang/sl/lang.php

lib/plugins/plugin/lang/sl/lang.php

lib/plugins/popularity/lang/sl/lang.php

lib/plugins/revert/lang/sl/lang.php

lib/plugins/usermanager/lang/sl/lang.php