structure.css -> default.css

Themes are optional, a theme overrides style in default.css

app/controllers/admin/purchases_controller.rb

@@ -64,10 +64,10 @@ class Admin::PurchasesController < ApplicationController
           design.layout.file = temp
           design.layout.to_save = true
           
-          title = design.structure_css_filename
+          title = design.default_css_filename
           temp = File.new(dir + '/' + title, 'w+')
           temp.write orig_zip.read(zip_name + '/' + title)
-          design.structure_css = temp
+          design.default_css = temp
           
           ['themes', 'javascripts', 'images'].each do |type|
             design.send(type).each do |object|