Update layouts for Jekyll 3

Layout metadata is now available via "layout", not via "page".

Author: stomar

_layouts/default.html

@@ -24,8 +24,8 @@
 
     <script type="text/javascript" src="/javascripts/jquery.min.js"></script>
     <script type="text/javascript" src="/javascripts/page.js"></script>
-    {% if page.javascript != null %}
-    {% for javascript in page.javascript %}
+    {% if layout.javascript != null %}
+    {% for javascript in layout.javascript %}
     <script type="text/javascript" src="/javascripts/{{ javascript }}.js"></script>
     {% endfor %}
     {% endif %}