adds rel canonical on main sections

app/views/layouts/application.html.erb

@@ -7,6 +7,7 @@
     <%= render "layouts/tracking_data" %>
     <%= render "layouts/meta_tags" %>
     <title><%= content_for?(:title) ? yield(:title) : setting['org_name'] %></title>
+    <%= content_for :canonical %>
     <%= stylesheet_link_tag    "application" %>
     <!--[if lt IE 9]>
       <%= stylesheet_link_tag "ie" %>