I wanted to use a regular <a>, but apparently rendering that many
anchors is too resource-intensive for Firefox, and it is noticeably
slower. It was even worse, in fact, because i had to have different
content for the main grid and the grid show in the new booking form,
as i did not want to have these links there, and had call a template for
each cell: 3 months × ~30 days × ~100 campsites = 9000 calls!
Using JavaScript for that is shameful, but it does not add much to the
existing markup, and no need for template fuckery.
I am using double-click to follow these links, instead of single click,
because it would be too easy to misclik on the grid, but that forced me
to add `user-select: none` to prevent the selection of text when double-
clicking.