CSS: Color icon-cancel red when hovered

refs #5543

public/css/icinga/main.less

@@ -98,6 +98,10 @@ table.listing-table {
   }
 }
 
+a:hover .icon-cancel {
+  color: @color-critical;
+}
+
 a.button {
   .button();
   display: inline-block;