implemented javascripts for wiki pages

public/javascripts/src/app/wiki_pages.js

@@ -0,0 +1,34 @@
+(function() {
+  Danbooru.WikiPage = {};
+  
+  Danbooru.WikiPage.initialize_all = function() {
+    $("#c-wiki-pages #preview").hide();
+    
+    this.initialize_preview_link();
+  }
+  
+  Danbooru.WikiPage.initialize_preview_link = function() {
+    $("#c-wiki-pages input[value=Cancel]").click(function(e) {
+      e.preventDefault();
+      window.back();
+    });
+    
+    $("#c-wiki-pages input[value=Preview]").click(function(e) {
+      e.preventDefault();
+      $.ajax({
+        type: "post",
+        url: "/dtext/preview",
+        data: {
+          body: $("#wiki_page_body").val()
+        },
+        success: function(data) {
+          $("#preview").show().html(data);
+        }
+      });
+    });
+  }
+})();
+
+$(document).ready(function() {
+  Danbooru.WikiPage.initialize_all();
+});