Allowing whitespace to wrap solves the issue of long link/button text awkwardly breaking out of controls
Widening desktop "pages" prevents some unnecessary wrapping in places like the "Create account" button on the login screen, whose content is slightly wider than it should be (but this is currently masked by the `nowrap`)
Closes https://github.com/bitwarden/clients/issues/2620
* 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`
