Test Stripe ACH integration

[JCBarry]

Without access to a Plaid/Stripe ACH account, this is difficult to test.

[JCBarry]

Override the plaid_exchange_token method in your callback controller to send the new account_id.

def plaid_exchange_token
  @plaid_access_token_response ||= Argyle.plaid_client.exchange_token(plaid_public_token, account_id: params[:account_id])
end