add missing js file

ponyconf/static/js/markdown-preview.js

@@ -0,0 +1,25 @@
+var csrftoken = $.cookie('csrftoken');
+
+function csrfSafeMethod(method) {
+  // these HTTP methods do not require CSRF protection
+  return (/^(GET|HEAD|OPTIONS|TRACE)$/.test(method));
+}
+$.ajaxSetup({
+  beforeSend: function(xhr, settings) {
+    if (!csrfSafeMethod(settings.type) && !this.crossDomain) {
+      xhr.setRequestHeader("X-CSRFToken", csrftoken);
+    }
+  }
+});
+
+$('a[href="#preview"]').on("show.bs.tab", function (e) {
+  $('#markdown-preview').html('Loading preview...');
+  var markdown = $('#markdown-content').val();
+  $.post(markdown_preview_url, {'data': markdown})
+    .done(function(data, textStatus) {
+      $('#markdown-preview').html(data);
+    })
+    .fail(function () {
+      $('#markdown-preview').html('Sorry, an error occured.');
+    });
+})