Add promotions code to core, backend + frontend where applicable

Move promotion_adjustments_spec to correct spot
An order should be able to ship when awaiting return and in the returned state

Fixes #2444
Improve styling for return authorizations index
Move states.js to backend
[backend] Add ror_ringer image necessary for images_spec
Fix results parsing for variant_autocomplete
Remove usage of old cleanTaxons method in taxon_autocomplete.js.erb