Revert "remove global danbooru object js in default layout"

This reverts commit 68e7de1fc4.

app/views/layouts/default.html.erb

@@ -71,6 +71,20 @@
   }
   </script>
   <script defer src="https://use.fontawesome.com/releases/v5.0.10/js/all.js" integrity="sha384-slN8GvtUJGnv6ca26v8EzVaR9DC58QEwsIk9q1QXdCU8Yu8ck/tL/5szYlBbqmS+" crossorigin="anonymous"></script>
+  <script>
+    if (typeof window.Danbooru !== "object") {
+      window.Danbooru = {};
+    }
+    window.Danbooru.notice = function(msg) {
+      console.warn("Danbooru.notice will be deprecated. Use $(window).trigger('danbooru:notice', msg) instead.")
+      $(window).trigger("danbooru:notice", msg);
+    }
+    window.Danbooru.error = function(msg) {
+      console.warn("Danbooru.error will be deprecated. Use $(window).trigger('danbooru:error', msg) instead.")
+      $(window).trigger("danbooru:error", msg);
+    }
+  </script>
+
 </head>
 <%= tag.body **body_attributes(CurrentUser.user) do %>
   <header id="top">