fix body overflow on dashboard

IPython/frontend/html/notebook/static/less/notebook.less

@@ -7,9 +7,12 @@
 @import "variables.less";
 
 body {
-    overflow: hidden;
     background-color:@notebook_background;
 }
+    
+body.notebook_app {
+    overflow: hidden;
+}
 
 blockquote {
     border-left: 4px solid #DDD;

IPython/frontend/html/notebook/templates/notebook.html

@@ -33,6 +33,7 @@ data-base-project-url={{base_project_url}}
 data-base-kernel-url={{base_kernel_url}}
 data-read-only={{read_only and not logged_in}}
 data-notebook-id={{notebook_id}}
+class="notebook_app"
 
 {% endblock %}