Nicer loading state

[glacials]

When the page has loaded but the JavaScript hasn't (whether slowness or network drop or JS blocked), the page displays all the Vue code that the JavaScript hasn't had a chance to hide yet.

We should at minimum hide this while loading. More complete options could be showing a layout "prediction" so there's less layout jumpiness when the load finishes, or even adding a build step that writes the correct sets into the static HTML file (maybe Vue pre-rendering exists?).