Fixes a bug in search-menu-results (type: "group"), where:
```javascript
const fullName = escapeExpression(group.fullName);
const name = escapeExpression(group.name);
const groupNames = [h("span.name", fullName || name)];
```
`groupNames` could end up having value "undefined" if a group doesn't have a `fullName`.
This will make a few minor improvements to the second factor user interface. Highlights include:
- Using the site's title to prefix the backup code filename. If non-ascii characters are detected, then prefix "discourse" instead.
- Add icons and change the text on some of the buttons for better clarity and consistency
- Add an education link to the security key modal
