Refactor Passwordable for 2.6+ or PHP5.5+

Huge cleanup.
Finally, the ugly workaround

    return (bool)$this->Auth->identify($request, $response);

goes overboard.
It directly uses PasswordHasher classes now.

It now also supports password_hash() from PHP5.5+ out of the box.
The only change needed would be

    'passwordHasher' => 'Tools.Modern'

I verified that the old blowfish way works when upgrading to this new hasher.