Retain API keys when a paper account is reset

[whitnable]

Currently, when a paper trading account is reset it also resets the API_KEY and the SECRET_KEY. This creates confusion, and a fair amount of support issues, because user trading programs then fail with the wrong key.

One solution would be to copy the key and secret key to the new account. If this is not possible, perhaps at least add a message indicating that the keys must be updated after an account reset.