Split return alerts for customer and carrier returns

Improved
New

Return notifications are now split by return type. Previously, Order returning and Order returned fired for every return, whatever the cause.

The four events are now:

- Order returned by customer
- Order returned by carrier
- Order returning (due to customer)
- Order returning (due to carrier)

A carrier return usually means a failed delivery you have to act on; a customer return often doesn't. Splitting the events lets you route each one to the right people.

To use it: choose your notifications per return type, for email and browser, in your notification settings