clean template: support negative delays (yes, they do happen every now and then)

<span class="countdown">

% if ($departure->{delay} and not $departure->{is_cancelled}) {

% if ($show_realtime) {

<span class="delaynorm">(+<%= $departure->{delay} %>)</span>

<span class="delaynorm">(<%= sprintf('+%d', $departure->{delay}) %>)</span>

% }

% else {

<span class="delay">(+<%= $departure->{delay} %>)</span>