Add a way to dismiss the omnipresent banner

I find the omnipresent banner very annoying. The color is very disruptive, and having it there in every page, every time I visit the platform, distracts me. I think Decidim should have a way so that users can dismiss the banner, so that it's hidden until the next time the banner is modified. We could store a value in localStorage via JS that holds a Hash of both the text and the link. Via JS we check that Hash: - If the Hash generated from the app data is the same we already have, the banner is hidden - If the Hash is different, the banner is shown