Fix ReadOnlyError when destroying StockItem

StockMovement is a readonly object so we can't delete them. And by that
logic I believe we shouldn't clear stock items from the database either
otherwise we will have stock movements associated with non existing
stock items

Fixes #3727
Fixes #3723
Revert "fix the ActiveRecord::ReadOnlyRecord exception when the @product is null when update the variant"

This reverts commit 8660b46a546418d91ffec02124303e13b1a7a6a8.
Revert "add spec to proof issue with variant update without product permalink."

This reverts commit f39a2f6a8c9435595245c47b9b2fb86a00db9f31.
Fix syntax error in product_property_fields
Prep for 2.0.5 release
admin menu spans all width and centers items since we removed horizontalNav.js from the backend we need a way to replicate the previous behavior display: table; on the parent <ul> and using display: table-cell; on chil <li> ensures we always use the whole width of the parent container and we span the children <li> accordingly using the same width across the given space

Fixes #3725
Do not generate a new identifier for a payment when it is re-saved

Fixes #3733
remove unnecessary semicolon in screen.css.scss

Fixes #3729
2 Migrations to ease in the upgrade from 1.3 -> 2.0 * Assign a shipping category to existing products & shipping methods if they don't have one * Migrate old shipping calculators to the new ones and preserve their preferences

Fixes #3605
Fixes #3660
[backend] Make checks for order totals more specific in specs

Probably fixes strange build failures like: http://ci.spreecommerce.com/viewLog.html?buildId=22440&buildTypeId=bt6&tab=buildLog
Product#stock_items should return stock_items for the master variant too

Fixes #3737

Conflicts:
	core/app/models/spree/product.rb
Add a default format if no format is defined in the locale file. Use the same default format as the datepicker gets in the translations partial.

Fixes #3602
While an order_id field exists within inventory_units, we should be able to retrieve these using an association

Fixes #3744

Conflicts:
	core/app/models/spree/order.rb
Add regression test for #3744
Associate user in Order `merge!` when possible

Users might be losing their cart changes when they come back but don't
visit either the /cart page or the /checkout

Fixes #3742
Fixes #3736
Fix path to cart.png

Fixes #3747
Bump to activemerchant 1.38.1
asset-url needs TWO arguments in this branch
Fix product paging issue

Fixes #2851
Fixes #3064

Conflicts:
	frontend/app/controllers/spree/taxons_controller.rb
Fix expectations in order/adjustments_spec so that it now passes