Raise ActiveRecord::RecordNotFound if order is not found on cancel page

Fixes #55
Fix an issue with old payment methods from the original paypal extension.

Signed-off-by: Nathan Lowrie <nate@finelineautomation.com>

Fixes #58
Make customisation of completion route simple

mirroring Spree::CheckoutController#update

Fixes #62
set InvoiceID to order number

Fixes #76
Add german translation

Fixes #79
Stop coffee_script and sass warnings
Pass cancel token back to checkout

Reasoning: as it is we lose the information that an order has been canceled. Better to keep it around so programmers can customise post Paypal failure cancellation experience.

Fixes #63

Conflicts:
	app/controllers/spree/paypal_controller.rb
Merge branch '2-0-stable' of https://github.com/spree-contrib/better_spree_paypal_express into 2-0-stable