Image in show view does not accept the width, the height and the prefix options

[devaneando]

According to the 'Resources/doc/show_view_types.md` file:

Available options

protected function configureShowFields(ShowMapper $showMapper)
{
    $showMapper
        ...
        ->add('picture', 'image', [
            'prefix' => '/bundles/acme/images/', // Image url prefix, default to null
            'width' => 75, // Image width, default to 50px,
            'height' => 75, // Image height, default to 50px,
        ]);
}

But the show template, does not have the prefix, the width and the height options available.

I fix this in the Pull Request #8

[OskarStark]

Looks good to me 👍🏻

[devaneando]

@picoss , DO you think it would be possible to merge this PR? I am using your bundle in a project I am working in, and this change, even being small, will help me a lot.