Slovak language update

inc/lang/sk/admin.txt

inc/lang/sk/conflict.txt

inc/lang/sk/denied.txt

inc/lang/sk/diff.txt

inc/lang/sk/draft.txt

inc/lang/sk/edit.txt

inc/lang/sk/editrev.txt

inc/lang/sk/index.txt

inc/lang/sk/install.html

inc/lang/sk/lang.php

inc/lang/sk/locked.txt

inc/lang/sk/mailtext.txt

inc/lang/sk/read.txt

inc/lang/sk/register.txt

inc/lang/sk/resendpwd.txt

inc/lang/sk/stopwords.txt

lib/plugins/acl/lang/sk/help.txt

lib/plugins/config/lang/sk/lang.php

lib/plugins/plugin/lang/sk/lang.php

lib/plugins/popularity/lang/sk/intro.txt