Fix spacing with heading/banner combination

Our CSS adjusts the spacing for the first `.heading-large` on the page
so that it aligns with the navigation. This doesn’t work when something
else comes first on the page, like a notification banner.

But since we only ever user `.heading-large` for the `<h1>`, and there
should only be one `<h1>` on the page we can just change the spacing
for _all_ `<h1>`s.

app/assets/stylesheets/app.scss

@@ -80,7 +80,7 @@ a {
 
 .column-main {
 
-  > .heading-large,
+  .heading-large,
   > .heading-medium {
     margin: 10px 0 15px 0;
   }