Only present promotion codes that have been applied in the admin interface, and use pluck rather than collect to load the promotion name and id

Fixes #5379
Fix spec broken by d0615f8
Fix variable css.
Bump active merchant and fix broken spec.

Conflicts:
	core/app/models/spree/payment.rb
	core/spec/spec_helper.rb
Fix spec.
Merge pull request #1 from spree/2-3-stable

2 3 stable