Only include css file once
I noticed it included many times on the run summary view
<?jelly escape-by-default='true'?>
<j:jelly xmlns:j="jelly:core" xmlns:t="/lib/hudson" xmlns:st="jelly:stapler">
+ <st:once>
<link rel="stylesheet" href="${resURL}/plugin/warnings-ng/css/custom-style.css"/>
+ </st:once>
<t:summary icon="${it.hasLargeImage() ? it.largeImageName : icon}">
<j:out value="${it.summary}"/>
