amended cgi scripts to handle service centre param to enable correct config file loading

moved hilis4 fastcgi run dir to /var for Debian server; removed extraneous timefmt ssi in index.html

new screen_category table; moved screens 'type' col to category_id; modified all screening terms & screening tests admin functions to accomodate new screen_category table; removed ajax validation from screen description & lab test field_label as these use 2 & 3-col unique keys so can't be validated by AJAX; email reports function uses users secure email address as sender; modifed portal_access function to supply SHA1 hash of current date - so failed login not sent back to portal page without explanation; modified mail_reports.pl to use item names instead of table id accessors