Print diplomas

Here's an MR that implements diploma printing.

While it's not perfect, I think it's better than nothing. Here a few things that could be improved:

• I'd love to get rid of the hard-coding of the A4, size, but I can't seem to figure out a good way that works in all browsers to make the diploma take up the entire page. width: 100vw; height: 100vh; works in Chrome, but not in Firefox (when printing).
• Perhaps make the number of placements to print configurable? Dunno, 3 seems pretty standard...
• Probably want some sort of integration with a configurable party-logo, like has been recently suggested by @steam0r

Neither of these seems critical, so perhaps we land this as-is soon?

Closes: #101 (closed)