Extend `CustomerWrapper` support for `TokenInterface`

Fixes #347
We can use the *logical not*, since the only *falsy* value possible here is `false`.

```php
    if (!($this->securityContext instanceof SecurityContectInterface)) { ... }
```

This is the preferred form. Also we might open an *RFC* about removing the parenthesis in the check, since `instanceof` has an **higher propity** than the logical not