rewrite pwg_mail_group() and pwg_mail_notification_admins()
new function pwg_mail_admins()
add complete template management in pwg_mail()
TODO : font-size problem in Thunderbird
git-svn-id: http://piwigo.org/svn/trunk@25357 68402e56-0260-453c-a942-63ccdbb3a9ee