* Change box-headers from generic `<div>` to semantic headings, tweak heading styles
Essentially, a late port to desktop of aspects from https://github.com/bitwarden/clients/pull/2223 (which I hadn't realised at the time also affected the desktop app)
* Change box headers in modals to `<h1>`s
* Fix/normalise modals
* Harmonise modal dialog headings, use `aria-labelledby`