Missing page navigation affordances on small screens

When viewing the notebook on small screens the pagination controls are reduced to just "Prev" and "Next" buttons. This means there is no way to:

1. See what page you are on and out of how many
2. Quickly jump to the first page
3. Quickly jump to the last page

(1) is the most important of these and (3) the least. How much (2) matters IMO depends on whether the Back button can easily be used to jump back a few pages to the first page. Currently that's not the case because we don't update the URL when you change pages.