Consider better focus handling when showing a dialog

[sivakusayan]

In a Clojure exercise, opening the "Settings" dialog should move focus into the dialog and prevent focus from moving into the blacked-out background of the dialog. Ditto for the dialog that appears when you successfully complete an exercise. This will make keyboard-only workflows less tedious.

Dialog (Modal) - ARIA Authoring Practices Guide

I don't mind taking a stab at this if you're okay with this.

[borkdude]

Sounds good to me, what about you @oxalorg ?

[oxalorg]

@sivakusayan Thanks that would be much appreciated!