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
Must set calculable before saving new calculator in MigrateOldShippingCalculators migration, otherwise MySQL screams
Temporarily make originator association available in UpgradeAdjustment migration
Add FreeShipping calculator back to ease migration from earlier Spree versions
Only remove spree_credit_card fields if they exist

I encountered a situation today on a database where these fields did not already exist. Best to have some kind of catch in place to not make the migration bomb out if the fields do not exist.
Use Spree.url() to add tokens to API calls to stock_locations

On 2.0, stock_locations AJAX class are getting a 401 on http://localhost:3000/admin/stock_transfers/new since securing the stock locations API end points.

Fixes #3828