Display credit cards under payments in orders/show [api]

They're displayed as payment source. Stores using custom payment sources
can customize the payment_source_attributes displayed in the api by
setting:

    Spree::Api::ApiHelpers.payment_source_attributes.push :attribute, :other_attribute
Sample should only create Store if none exists yet

There's a migration which already create a store record. Creating it
again on the samples breaks the spree install due to validation on
Store#code uniqueness
Do not attempt to create a store with 'spree' code if one already exists
[backend] Always show 'Tracking' label on shipments

A couple of the backend specs were failing because this label wasn't around
Revert "[backend] Always show 'Tracking' label on shipments"

This reverts commit cab88fa391244fa02ca74a1eb3c1b88c26d8394b.
Replace Spree::Config[:site_name] with Spree::Store.current.name.

This gets rid of the millions of deprecation warnings in the rspec
output.
Add failing test showing payment processing is set in a transaction.
Turn off transactions around Spree::Order state transitions.
Mark test of subclassed order as pending.

This test is now failing but it is unclear if it was ever really
testing what it claims to be testing. An order with no email
is not valid and should not save, so the test should not pass.
Add changelog entry.

Fixes #4542
Use Monetize.parse extracted from Money

We originally included these functions in Spree::Money when they became
deprecated in ruby-money. They are now available in the monetize gem.

Fixes #4529
Dont show out of stock for master product

We only care about variants stock for a product with variants
Introduce PaymentMethod#reusable_sources

General method which custom gateways will probably override to make it
possible reuse payment sources

Fixes #4450
Drop pending examples in order_contents_spec
Move api/products_controller logic to a Importer

Allow us to easily apply that same logic in other parts of a Spree
application. Plus clean up some duplicated code
Use sql rather than zone.include? method to find matches.

In applications with a large number of tax zones recalculating tax is
extremely slow.  In my particular instance transitioning form the
address to delivery step of checkout was taking up to 15 seconds, and
this change cut that in half.

Transition from Address to Delivery - Before:
Redirected to /checkout/delivery
Completed 302 Found in 14107ms (ActiveRecord: 252.5ms | Elasticsearch:
0.0ms)
Completed 302 Found in 13524ms (ActiveRecord: 195.2ms | Elasticsearch:
0.0ms)

Transition from Address to Delivery - After:
Redirected to /checkout/delivery
Completed 302 Found in 5423ms (ActiveRecord: 178.4ms | Elasticsearch:
0.0ms)
Completed 302 Found in 6223ms (ActiveRecord: 212.2ms | Elasticsearch:
0.0ms)

I’d like to figure out how to improve this even more, but cutting time
in half with this small change is a good start.
Remove Order#exclude_tax? as it is not used anywhere.
Scope tax rates to the orders tax zone.  Cuts my address to delivery transition from 6 seconds to 1 second
Removing bigdecimal/util require that was needed for ruby 1.8 support

Fixes #4551
Revert "Scope tax rates to the orders tax zone.  Cuts my address to delivery transition from 6 seconds to 1 second"

This reverts commit c9de5910d811c3d8c628fe4b70852033795a4ae7.