chore: define alt ng2 layout for top-level pages (#2686)

public/_layout.jade

@@ -1,3 +1,13 @@
+if jade2ng
+  if hero == 'home'
+    != partial("/_includes/_hero-home")
+  else
+    != partial("/_includes/_hero")
+    != partial("../_includes/_banner")
+  - var format = autoformat ? 'docs-content' : ''
+  article(class="l-content #{format}")
+    != yield
+else
   doctype html public
   html(lang="en" ng-app="angularIOApp" itemscope itemtype="http://schema.org/Framework")
     head