Add Preview to templates-sdk develop nav and global nav in templates-sdk-dev. Remove dependence on -includePreview.

Change-Id: I1456c3c94522f58c7d1c899ff96dd95cdc6ada7c
diff --git a/tools/droiddoc/templates-sdk-dev/docpage.cs b/tools/droiddoc/templates-sdk-dev/docpage.cs
index 7f53e6f..ab5fb40 100644
--- a/tools/droiddoc/templates-sdk-dev/docpage.cs
+++ b/tools/droiddoc/templates-sdk-dev/docpage.cs
@@ -36,6 +36,7 @@
       if:wear ?> wear<?cs /if ?><?cs
       if:tv ?> tv<?cs /if ?><?cs
       if:auto ?> auto<?cs /if ?><?cs
+    elif:(preview) ?> preview<?cs
     /if ?><?cs
     if:page.trainingcourse ?> trainingcourse<?cs /if ?><?cs
 /if ?>" itemscope itemtype="http://schema.org/Article"><?cs