Add back blank layout

- The new maintenance page will use a blank layout that does not have a
footer because we don't want users thinking they can click on a link
that will just lead back to the maintenance page

webapp/layouts/blank.vue

@@ -0,0 +1,17 @@
+<template>
+  <div class="layout-blank">
+    <ds-container>
+      <div style="padding: 5rem 2rem;">
+        <nuxt />
+      </div>
+    </ds-container>
+    <div id="overlay" />
+  </div>
+</template>
+
+<script>
+import seo from '~/mixins/seo'
+export default {
+  mixins: [seo],
+}
+</script>