Create better unique token

This creates a better token with more security of the token and more reliable for unique token.
I know that every token generation is different, but if we're going to use SHA we probably want to use `drupal_hmac_base64` to ensure encoding compatibility.

```php
$uid = $account ? $account->uid : '';
return drupal_hmac_base64($account->uid . drupal_get_hash_salt(), $unique);
```
Also note that since the default for `$account` is `NULL` we need extra checks. We can also dump the `secretTokenPrefix` in favor of Drupal's salt.