Remote erb inline comment from backend/payment_method/form

Motivation is to avoid parse errors when trying to deface that file

See #3913
use a better name for the method that restarts the checkout flow,also make sure we use the checkout_steps.first instead of hardcoding it to "address".

use expect syntax

use the correct syntax

Conflicts:
	core/app/models/spree/order.rb

Fixes #3995
(backend) in order details, line items states could not be translated

Fixes #4009
[backend] verifying if product picker returns any product

Fixes #4008
do not call move_to_child_with_index when the taxon is new, since this
is not supported by acts_as_nested_set.

Fixes #3999
[backend] Use Shipment#display_cost rather than #cost
Bump kaminari to 0.15.0
Go with whatever money gem activemerchant depends on