handle empty products set on cache_key_for_products

Conflicts:
	core/app/helpers/spree/products_helper.rb
rely on maximum return to fall back on static date

Fixes #4565
Add Date string to caching/products_spec
Set RAILS_ENV=test on rake test_app

Got weird issues while building dummy apps in extensions because the
dummy development db, which we don't really care about, was not being
dropped and migrations would always fail
Use routing concern for api/config/routes.rb
Merge pull request #4590 from spree/refactor-routes

Use routing concern for api/config/routes.rb
Refactor Shipments API & JS.

Conflicts:
	backend/app/assets/javascripts/spree/backend/shipments.js.erb
Remove deprecated orders/shipments api.