Updated and added 'pl' language files

--HG--
rename : plugins/blog/languages/en.lang.php => plugins/blog/languages/pl.lang.php
rename : plugins/box/dashboard/languages/en.lang.php => plugins/box/dashboard/languages/pl.lang.php
rename : plugins/box/emails/languages/en.lang.php => plugins/box/emails/languages/pl.lang.php