api/orders_controller#empty: now uses empty!

this is consistent with frontend/orders_controller

[Closes #3611]
change html lang attribute for admin layout depending on locale
Default to quantity 1 in `order.contents.add`

[Closes #3606]
Adding test cases for Default to quantity 1 in `order.contents.add`

[Amends #3606]
Improve message for missing shipping rates in checkout

[Closes #3590]
It feels pretty weird to have a default message that tells the customer
to "choose a different shipping address". I think we should just tell
explictly that the store cannot come up with any shipping rate. That
might be either because the shipping address is not covered or that the
taxes associated with products in cart are not properly associated with
any shipping method
Improve cart page rendering:
- Render line_items collection in partial rather than looping
over line_items and rendering the partial multiple times

Fix #3609
Set created_by for orders when associating with a user IF the created_by value is blank.  Add specs for both cases.

Fixes #3614
initial port from 1-3-stable of spree order import api, updated for stock and adjustment states

Fixes #3617
Ensure order is refreshed before returning json
Fixes outdate jQuery live.

Remove colons for label tags for consistency in layout.

Add missing required for field in prototypes form.

Fixes taxon form layout issues.

- Add JS function that update info tag when typing permalink.
- Add space to required (still form don't get validated).

Remove loose p-tag in taxonomies index page.

Nicer products stock delete icons.

It still need its own delete js even because rows are nested and don't
gets fully deleted.

Fixes wild placed sorting icons.

Misc table layout styling.

Fixes #3619

Conflicts:
	backend/app/views/spree/admin/orders/customer_details/_form.html.erb
	backend/app/views/spree/admin/products/stock.html.erb
Allow users to dont split packages

By making the Packer know how to deal with an empty splitters array we
allow users to set

    Rails.application.config.spree.stock_splitters = []

in theirs apps so that packages will never be split

Fixes #3618
Fix confirm option deprecation.
Introduce better approach for regenerating shipments

Instead of recreating shipments every time customers change order items
it only destroy shipments, if any exists, and put order state back into
address so users are forced to transition the order again from address
to delivery and still recreate shipments properly

Another minor change on CheckoutController was necessary. We need to run
`setup_for_current_state` only after all other checks are done. e.g.
authentication, valid order state. This is so that customer don't get
their items removed by the Differentiator. Current specs should cover
all possible scnearios I could think of.

Fixes #3497
Fix conflict.
Remove ForbiddenAttributesProtection module from Order

Left over from master rebase on rails4 branch, we don't need that any
longer

Fix #3553