After submitting this PR I discovered an inconsistency with watching first post that I am not sure how to resolve.
Watching first post exists in two primary locations: the notification level dropdown on category pages, and the user preferences page.
The User Preferences page appears to be a handlebars template which uses the
watching-first-post for the class, following what appears to be the Discourse convention of using hyphens for CSS classes.
watching_first_post for the class, following what appears to be the Discourse convention of using underscores for translation files.
Which is correct? At the moment, to target the watching first post icon in all locations, two selectors are needed, which seems less than ideal. Can this be resolved so the icons share the same CSS class, without breaking CSS or translation conventions?