Localized collection editor and support inbox endpoints

Localized collection editor

The collection editor is fully localized: labels, hints and validation messages all come from the translation catalog, so a merchant running admin in another language no longer runs into English-only strings halfway through building a collection.

Customer support inbox endpoints

Support conversations are readable and writable over the public API. Teams already running a helpdesk can pull store messages into it, or push replies back, without a person sitting in two inboxes.