Followup to e37fb3042d
Some plugins like discourse-ai and discourse-saml do not
nicely change from kebab-case to Title Case (e.g. Ai, Saml),
and anyway this method of getting the plugin name is not
translated either.
Better to use the plugin setting category if it exists,
since that is written by a human and is translated.
1. Use `this.` instead of `{{action}}` where applicable
2. Use `{{fn}}` instead of `@actionParam` where applicable
3. Use non-`@` versions of class/type/tabindex/aria-controls/aria-expanded
4. Remove `btn` class (it's added automatically to all DButtons)
5. Remove `type="button"` (it's the default)
6. Use `concat-class` helper
In some languages, labels on the site settings navigation menu
get truncated. This adds titles to menu items, so users can see
untruncated labels on hover.
