Renders the "hot", "new" and "journal" tabs, and "followed" for a signed-in user. A tab leads to the same scope: /new for every dump, /music/new for a category, and the viewer's default tab to the bare / or /music. A tab is a view of the same page, so it takes the place of the current history entry, while picking a category, another page, adds one and keeps the tab and its view, from /music/follow/playlists to /cinema/follow/playlists. Index renders it twice, in the header and below it, and CSS shows one by screen width.