Wamp session IDs are insecure
WampConnection classes use `uniqid()` to [generate an identifier](https://github.com/ratchetphp/Ratchet/blob/master/src/Ratchet/Wamp/WampConnection.php#L20) that is later used by the user. This function gives fairly predictable strings (there's even a warning on the [official PHP docs](http://php.net/manual/en/function.uniqid.php)) and shouldn't be used for this purpose.

Preferably session identifiers would be generated using something like `openssl_random_pseudo_bytes` or another safer PRNG.
