Add all status codes that BigCommerce say they may return

Hey, 

I’ve done this from the list at https://developer.bigcommerce.com/api/status-codes

When I was adding codes, I noticed that they apparently don’t return 502, so I removed this in a separate commit – I guess just because the docs don’t say they’ll return it doesn’t mean that they (or a proxy?) definitely _won’t_ return it in practice, so you might want to leave it in there to be ‘defensive’. No sweat either way.

Chris