Give ShippingCategory correct name so sample shipments have shipping_rates

Fixes #3795
Support .name and .description on line items

This allows line_items to override and control what should be used for
description and name sanely.

The extra helper isn't ideal, but we do maintain the old interface for
extensions.

Fixes #3734
Do not allow one product to be assigned the same taxon more than once

Fixes #3494
Include jquery.validate localization messages when the locale is not :en

Fixes #3794

Conflicts:
	frontend/app/views/spree/checkout/edit.html.erb
[backend] Add missing adjustments/_adjustment partial
Add a test for #3494
Allow users to delete country via backend UI

Fixes #3807
Allow users to create new countries via backend UI

Fixes #3807
Move spree/shared/address partial into frontend

That's the only place Spree uses it

Related to #3758
Clean up backend address forms

Related to #3758
With the change of shipping categories seed to Default, product seed needs to match. References #3795

Fixes #3811
Re-instate DefaultTax calculator's ability to calculate for an order

This needs to be supported for legacy reasons. Orders coming from Spree 2.1 and older have the tax adjustments applied on the order as a whole.
Add migrations to migrate old adjustments to new adjustments system

Part of the work in #3567
Remove binding.pry
Allow recreating deleted stock items

Add deleted_at to uniqueness scope otherwise use cant recreate a stock
item on the same stock location

Fixes #3834
Prefs: don't determine persist? from .connected?

.connected? returns false until a connection is actually attempted. This
meant if the cache was empty, preferences would be set to their default
values and that would be persisted to cache.

This reverts commit 9ca8ef97fb9139a5aecd1f406b21a7fadfdca658.

Fixes #3785
prefs: don't cache fallback when not persisting

When persistence was disabled (for whatever reason), fallback values
were written to the cache if there was no existing value cached.

There is no benefit in doing this. Database lookups will not happen
without persistence being enabled, and there was potential for the
fallback values being incorrectly written to the cache.
Add maximum length validation for promotion description [Fixes #3837]
verify if a user can fire a following event on order or not

Fixes #3818
Reload rules select2 box after picking a PromotionRule

So that the chosen rule no longer is displayed on the select2 box, users
can associate each rule only once with the promotion

Fixes #3572
Fixes #3816