How to insert a HTML snippet/widget/shortcode/partial into blog post contents?

I would like to create a HTML widget with variable title and insert it into multiple blog posts contents using the WYSIWYG editor. For example I want to add to the post body:

{{> banner title=”Buy now!”}}

But how to do it? Should I make a helper (.js) or a partial (.hbs)? How to tell Publii to include the HTML snippet in place of the shortcode? Is it possible to add a button to the editor toolbar which will insert my widget (like e.g. gallery, media)?

Thanks in advance!