Add Spree::Admin::RootController for redirecting purposes.

Currently, is really difficult to redirect to a different tab when the
user has logged in if said users cannot at least :admin, :index
`Spree::Order`s.

This commit adds a controller that handles `/admin` route so anyone can
easily redirect to another page (or implement any other logic).
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.
Close a table in variant autocomplete

There was no table closing tag in the variants autocomplete.
Fixes #5396
data-hook for form

Fixes #5397
Right no objects found message for new stock transfer
Fixes #5400
Deleted the ajax_indicator for the observe_field on change

Deleted the spinner from the states index
Fixes #5402
Added configuration_menu to the 'add country' page
Fixes #5403
Added configuration_menu to the 'stock locations edit'

Added configuration_menu to 'stock locations new'

Fixes #5404
Fixed objects name for stock location form labels
Fixes #5406
Fix translation
Fixes #5408
Code for tax category.

Fixes #5409
add array & hash option for spree preferences

Fixes #5405
Fixes #5002
Dont let order import fail silently on bad line items.