Added new database-class based on PHP-PDO to use prepared-statements; implemented new Database-class in admin_index (more to follow, old DB class still in use everywhere else); secure standard_error back-link output

Signed-off-by: Michael Kaufmann (d00p) <d00p@froxlor.org>
Merge branch 'master' of github.com:Froxlor/Froxlor