Add pickup date

This additional date helps users to find the correct order if the time
between end and pickup varies a lot.

db/migrate/20160217152621_add_pickup_to_order.rb

@@ -0,0 +1,5 @@
+class AddPickupToOrder < ActiveRecord::Migration
+  def change
+    add_column :orders, :pickup, :date
+  end
+end