Add a sticky div to the 'Package details' page that will keep the name of the Package visible when the user scrolls

The title says it all. I already wrote the HTML and CSS code for this earlier today -- for an initial draft, at least -- and will start with that when I tackle this issue.

One question: do we want or need a non-white background? A thick bottom border or a bottom box-shadow will make the div more visible when it rests at the top of the page, but we will also have two more rows below it, newly added in my work on issue #1228, which I had contemplated displaying as a 3-row table -- we might have a design/display conflict to resolve when we reach this point.