Created center_die function in errors.php

Created the center_die function in errors.php which serves as an
alternative to the die function. It does mostly the same thing except
in includes the styles defined in the templates instead of showing just
a white boring page
Created the errors module which is included by the center_die function

The errors module should preferably only be used by the center_die
function. If there is a need to show an error page, a call to
center_die should be made instead
Changed index.php to call center_die instead of die