add references to user.css in all templates

contrib/templates/default/newboard.mustache

@@ -2,6 +2,7 @@
   <head>
     <title>create new board</title>
     <link rel="stylesheet" href="{{prefix}}static/site.css" />
+    <style src="{{prefix}}static/user.css" type="text/css" />
     <script type="text/javascript" src="{{prefix}}static/newboard.js">
     </script>
   </head>