First implementation of password and salt generation

Add you can try to test that you register the compiler pass to : 

```php
function it_register_salt_generator_pass(ContainerBuilder $container)
{
    $container->addCompilerPass(Argument::that(function ($pass) {
        return is_object($pass) && $pass instanceof SaltGeneratorPass;
    }))->shouldBeCalled();

    $this->build($container);
}
```