Add ViewOnly widget class to pass options

[quintenbuis]

This PR adds a ViewOnly class that takes the view name as the render method argument and passes options to that view.

Before the widget config option must follow the following structure:

'widgets' => [
    'Magento\Cms\Block\Widget\Block'                   => Rapidez\Core\Widgets\Block::class,
],

Now instead mapping the Magento block to a full class string you can pass a view name and it will grab the view_only_widget class in the config and render the view:

'widgets' => [
    'Magento\Cms\Block\Widget\Block'                   => 'widget-with-options-view',
],

The ViewOnly class can also be customized in the config:

'view_only_widget' => \Rapidez\Core\Widgets\ViewOnly::class,

[royduin]

Thanks! 💯 Docs: https://docs.rapidez.io/0.x/extending.html#widgets