Make use of Security::salt() instead of Configure::read('Security.salt')...

After a recent update i got an error while reading data through the CookieComponent.
`Invalid key for decrypt(), key must be at least 256 bits (32 bytes) long.`

The error has been introduced by calling Configure::consume('Security.salt') in app/bootstrap.php here:
https://github.com/cakephp/app/blob/master/config/bootstrap.php#L135

By searching for 'Security.salt' in all cake's source folder I found that in other places there is the same problem.