Migrate all reusable credit card to wallet sources

The behaviour prior to adding the Wallet was to allow reuse of any
CreditCard which had a payment profile. However the migration was only
migrating CreditCards marked "default".

This now migrates all credit cards with an associated
gateway_customer_profile_id.

This also no longer removes the "default" column from the credit card,
as we decided this was safer to leave in for at least one release.

core/db/migrate/20160420181916_migrate_credit_cards_to_wallet_payment_sources.rb

@@ -0,0 +1,26 @@
+class MigrateCreditCardsToWalletPaymentSources < ActiveRecord::Migration[4.2]
+  class CreditCard < ActiveRecord::Base
+    self.table_name = 'spree_credit_cards'
+  end
+  class WalletPaymentSource < ActiveRecord::Base
+    self.table_name = 'spree_wallet_payment_sources'
+  end
+
+  def up
+    credit_cards = CreditCard.
+      where.not(gateway_customer_profile_id: nil).
+      where.not(user_id: nil)
+
+    credit_cards.find_each do |credit_card|
+      WalletPaymentSource.find_or_create_by!(
+        user_id: credit_card.user_id,
+        payment_source: credit_card
+      ) do |wallet_source|
+        wallet_source.default = credit_card.default
+      end
+    end
+  end
+
+  def down
+  end
+end