Add `ship_total` to api order_attributes
Make api helper attributes class attributes

To make it easier to append more attributes. Other applications /
extensions can append their own stuff without having to override
methods. e.g.

        Spree::Api::ApiHelpers.order_attributes.push :locked_at
Make OrderInventory aware of `track_inventory_levels`

It should not create backordered inventory units when it is set `false`
use the new Spree logo [Fixes #3975]
Update all adjustment types

In f9ed99a the order updater was changed to update only shipping
adjustments and promotion adjustments. This was done so that the
in-memory order was used for promotions calculations.

This broke some extensions which expected their custom adjustment types
to receive updates.

This goes back to the previous behaviour of updating all adjustments,
but uses the in memory order object if it is the adjustment's source.

Fixes #3961
Use update_columns rather than update_attributes_without_callbacks
Need to use real order in payment_spec
[api] Do not call object_params twice within CheckoutsController

Fixes #3965
update adjustment_count in reports_spec as the very last thing

This stops the tests from breaking. Everyone goes home happy.
Replaced Taxon :position refs with :child_index=

Fixes #3390
Fixes #3956

Taxon position unnecessarily fights against the awesome_nested_set
API. By using a_n_s's :move_to_child_with_index method we can more
fully leverage acts_as_nested_set.

Conflicts:
	core/app/models/spree/taxon.rb
	core/spree_core.gemspec
Not attempting to reorder taxon on create since awesome_nested_set refuses
Shorten end-waterfalls in TaxRate spec

Mainly because it annoyed me.
Tax rates such as GST now apply an 'included' Adjustment

This is to say that there was an adjustment to the object, but that adjustment is included in the price of that object.
Cache tax_total in the database to save it being recomputed every single time
No need for dependent + ordering options on Order#all_adjustments

Dependent destroy will be taken care of by the real adjustments' parents, and ordering is non-important for what this is used for (which is only calculating tax totals atm)
Bump to activemerchant 1.42.2
Add missing migration for adding included to adjustments
Add Adjustment included + additional scopes
Permit last_digits to be sent through on the checkout

This is necessary for the Stripe gateway in spree_gateway
Use destroy_all for all_adjustments in tax_rate spec so that adjustments are actually removed from database

delete_all just disassociates the adjustments from the order objects by setting order_id to nil