Paypal merchant permissions ui

I'm having a bit of hard time following the flow here. How about something like this?

```ruby
if (params[:verification_code].present?)
  # Only call this command if we have a verification code. The contract of command
  # is ideally that it requires you to pass valid parameters and raises an error
  # if you pass nil for required parameter.
  MarketplaceService::PaypalAccount::Command.confirm_pending_permissions_request(
    @current_user.id,
    @current_community.id,
    params[:request_token],
    params[:verification_code]
  )
else
  flash[:error] = t("paypal_accounts.new.permissions_not_granted")
end

# Let show/new take care of cleanup of unverified permission requests etc.
redirect_to new_paypal_account_settings_payment_path(@current_user.username)
```