Allow shipped_email to take either a shipment id or a shipment object

Fixes #54
Account for case where OrderMailer methods can receive an order or order ID

Related to #54
Bump Capybara to 1.1.4
Add backend, frontend + API as dependencies
Fix to order and shipment mailers.

Fixes #55
Merge branch 'master' into develop

Conflicts:
	spree_multi_domain.gemspec