Add `SideBar` component

[tim-x-y-z]

hi thanks for the great library, it would be great if we were able to get the navbar on the side, and potentially with appearing / disappearing option. maybe something like: https://getbootstrap.com/docs/5.0/examples/sidebars/#

[samuelcolvin]

The problem with components like this is that they have to be responsive, and it's not easy to generalise responsive design without anointing a specific frontend library.

Still, I'm happy to review a pr if someone comes up with an idea.