Implemented: FS#3150 - Add description text to spamfilter levels

interface/web/mail/form/spamfilter_blacklist.tform.php

interface/web/mail/form/spamfilter_users.tform.php

interface/web/mail/form/spamfilter_whitelist.tform.php

interface/web/mail/lib/lang/de_spamfilter_blacklist.lng

interface/web/mail/lib/lang/de_spamfilter_users.lng

interface/web/mail/lib/lang/de_spamfilter_whitelist.lng

interface/web/mail/lib/lang/en_spamfilter_blacklist.lng

interface/web/mail/lib/lang/en_spamfilter_users.lng

interface/web/mail/lib/lang/en_spamfilter_whitelist.lng