Use dynamic error pages built through the asset pipeline

Fixes #1241

app/controllers/errors_controller.rb

@@ -0,0 +1,15 @@
+class ErrorsController < ApplicationController
+  layout "error"
+
+  def forbidden
+    render :status => :forbidden
+  end
+
+  def not_found
+    render :status => :not_found
+  end
+
+  def internal_server_error
+    render :status => :internal_server_error
+  end
+end