Add Print icon to slide view

It redirects the user to the print view of the document. I claim that
people should either be smart enough to use ctrl+P or ask someone who
knows how to print a webpage. I don't want to babysit our users.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

public/js/slide.js

@@ -14,6 +14,7 @@ window.lastchangetime = window.lastchangeui.time.attr('data-updatetime')
 updateLastChange()
 const url = window.location.pathname
 $('.ui-edit').attr('href', `${url}/edit`)
+$('.ui-print').attr('href', `${url}?print-pdf`)
 
 $(document).ready(() => {
     // tooltip