stripe: Handle a customer being deleted.

[elliotcourant]

If the customer is deleted in Stripe then this error is seen the next time the user tries to make an API call.

[elliotcourant]

Added handling of the customer.deleted webhook in 9db1e73

This will just set the customer Id to nil. This way a new customer gets created the next time the customer tries to use their account.

[elliotcourant]

this did not fix the problem

[elliotcourant]

New Problem; stripe can sometimes deliver webhooks in the wrong order. Since we only assert whether or not a subscription is active based on the last received webhook we cant handle this properly right now.

The update subscription webhook had the active status which is correct, but we received the create subscription webhook after it. The create subscription webhook had an "incomplete" status which broke the subscription state.

[elliotcourant]

I've fixed the problem with webhooks being delivered in the wrong order. But still need to verify the behavior when a customer is deleted.