Remove append_view_path from api ControllerSetup

That line was preventing us from overriding templates within other
application or extensions

Fixes #3450
Shipments need to check if they can get rates

before trying to get them, a private method
has been added to check if the shipment is ready
to get rates, currently it only checks if the order
has set a shipping_address, if theres custom business
logic for a specific store this is what they should
be customising instead of the refresh_rates call
which is already getting too complicated by itself.

Added tests for this and had to include a before call
to stub this same call in order for the other tests to pass.

fixes #3848
fixes #3849
Simplify `can_get_rates?` in Shipment
Reference Spree::Order to prevent error
Revert "Remove append_view_path from api ControllerSetup"

Since Api::BaseController inherits from ActionController::Metal we do
need to use append_view_path for rendering views inside api/app/views
and the main app views dir

Extensions should probably also use append_view_path themselves if they
want to override an api template

This reverts commit b0378f5f73927d40a34acb8777b004957588e1aa.
Remove duplicated responder configs and include from api

ActionController::Rendering already includes
AbstractController::Rendering and we had duplicated respond_to calls
in basecontroller and controller_setup
Remove some dead order admin javascript

The element referred to was removed in 72e5d47

Fixes #3872
Bump to allow any highline version in the > 1.6.18 & < 1.7.x range

Fixes #3870
Remove order.rb.swo file
Fix issue where Product#set_property was causing an undefined method with spree_i18n

Fixes spree/spree_i18n#301
Select2 fixes to center the search box

Fixes #3854
Fixes #3863
Order state changes are now tracked after all transitions, exactly like shipments and payment state transitions

Fixes #3850
Allow coupon codes to be added from admin adjustments index.

Fixes #3859
Fix AdjustmentsHelper#display_line_item showing empty brackets if a variant had no options text
Fix pluralization issues with translations + views for CreateItemAdjustments action
Add translation for FreeShipping promotion action
Remove Promomtion#order_activatable in favour of the class method of the same name
checkout/registration view should live in auth component, not frontend
Bump activemerchant to 1.40.0

Likely fix for spree/spree_gateway#105
Fixed jquery.payment formatting not applying to more than one set of gateway fields on the payments page

Conflicts:
	frontend/app/assets/javascripts/store/checkout.js.coffee