mail: Include shipment details in the shipping method

Allow to explain the shipping method. This is used in the shippment
mail. E.g. one can explain the registered mail and the options.

app/views/admin/dhls/_method_details_form.html.erb

@@ -0,0 +1,6 @@
+  <%= f.field_container :details do %>
+    <%= f.label :details, t("details") %><br />
+    <%= f.text_area :method_details  %>
+    <%= error_message_on :shipping_method, :method_details %>
+  <% end %>
+

app/views/shipment_mailer/dhls/_tracking_description.text.erb

@@ -0,0 +1 @@
+<%= @shipment.shipping_method.method_details %>

db/migrate/20120801104503_dhl_shipping_details.rb

@@ -0,0 +1,9 @@
+class DhlShippingDetails < ActiveRecord::Migration
+  def self.up
+      add_column :shipping_methods, :method_details, :string
+  end
+
+  def self.down
+      remove_column :shipping_methods, :method_details
+  end
+end

lib/sysmocom_dhl_hooks.rb

@@ -6,4 +6,8 @@ class SysmocomDhlHooks < Spree::ThemeSupport::HookListener
 
   # Add the DHL label download
   insert_after :admin_shipment_edit_buttons, 'admin/dhls/address_label'
+
+  # Add shipment identification..
+  insert_after :shipment_mailer_shipped_email_tracking, 'shipment_mailer/dhls/tracking_description'
+  insert_after :admin_shipping_method_form_fields, 'admin/dhls/method_details_form'
 end