Removed empty translation entries.

We should actually look into doing a comprehensive audit of translation keys before going to Spree 2.0 to remove anything that is no longer needed.  For instance, do we still need the translations related to product scopes/groups?
Extract taxonomy jstree menu to a new file

Fixes #2953
Call state_machine at the top of Spree::Shipment class
[backend] Fix 'order_has_no_payments' key in payments/index
After updating customer details, ensure state is transitioned as far to 'complete' as is possible

Fixes #2950
Fixes #2433
[backend] Fix order URL reference in payments controller