Added failed state to the admin variables

A payment state could be `failed`.
This state was missing from the admin variables.
The payment state had no color, it was just a blank circle. I added the red color.
I noticed this in spree 2-2-stable.

Fixes #5378
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
Don't process refunds created with a transaction_id

If a transaction id exists, presumably it has already been processed.
This comes in handy when migrating over records from another system.

Fixes #5381
Bump active merchant and fix broken spec.
add select2 call after loading new images
Fixes #5385
we fixed mail validator.
set the order#payment_state to the correct state when order is canceled

Fixes #5278
Closes #5279
Closes #5388

return the new payment state in the update_payment_state, and add some spacing in the spec.

remove the stub to make sure this is not always returning "pending" *doh*
Update readme for rails version.