Refactoring digital shipping calculation and display

* removed the deface override that modified the checkout/_delivery partial
* created custom digital delivery calculator
* removed digital_shipping_method from Spree::Order. Moved logic to available_shipping_methods monkey patch

The main goal was to eliminate the shipping method detection logic from the _delivery partial.
This was a bit of a hack all along and didn't really present the correct information to the underlying
order logic (i.e. rate_hash.blank? would return true when there was no shipping options available).
This should be more future proof and make overriding another aspect of the delivery process easier.

lib/spree_digital/engine.rb

@@ -4,14 +4,13 @@ module SpreeDigital
 
     config.autoload_paths += %W(#{config.root}/lib)
 
-    # Use RSpec for tests
-    config.generators do |g|
-      g.test_framework :rspec
-    end
-    
     initializer "spree.spree_digital.preferences", :after => "spree.environment" do |app|
       Spree::DigitalConfiguration = Spree::SpreeDigitalConfiguration.new
     end
+
+    initializer "spree.register.digital_shipping", :after => 'spree.register.calculators' do |app|
+      app.config.spree.calculators.shipping_methods << Spree::Calculator::DigitalDelivery
+    end
    
     def self.activate
       Dir.glob(File.join(File.dirname(__FILE__), "../../app/**/*_decorator*.rb")) do |c|