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