Getting ready for Teatro.io stage server
Merge pull request #5067 from semenyukdmitriy/teatro_stage

Getting ready for Teatro.io stage server
Validate uniqueness of order numbers... Why was this FIXME never fixed until now... Fixes #5102
Add `Spree::Promotion#products` back.

Currently used in the frontend.

Closes #5071
Add mail_from_address field to general settings page

Closes #5047