fix permalink handling to force uniqueueness and rename on product destroy

Fixes #4805
Make migration more tolerant of deleted Variants

This migration bailed for me when it found an old order (before Spree used `acts_as_paranoid`) with a line_item referencing a Variant that no longer existed.

Making the migration use `variant_id` instead of `variant.id` fixed this problem for me, and I suspect will make the migration path smoother for other people who have been using Spree since before the `paranoia` gem.

Fixes #4822
Bump activemerchant to 1.43.1

This should fix spree/spree_gateway#149
Don't assume default variant in JS. Let this be controlled by HTML markup.

Fixes #4849
Downcasing locale for jquery.validate i18n messages

Fixes #4867
Added initSelection to variant_autocomplete

Fixes #4862