Help new users discover the features available in the archive browsing view

The archive browsing view is feature rich. Once a new user is shown how to use a feature, it is immediately understood, but there are seveal features that are non obvious until shown, like the Permalinks tab and the way to select a code fragment by clicking+shift-clicking on the line numbers.

Best practice in modern web applications is to offer newcomers a "guided tour" with popups that highlight the different non obvious features. This guided tour can be disabled when the newcomer had enough. It is helpful to also add a way to take the tour again if needed.

---

Migrated from T3202 (view on Phabricator)