40C3: tours, schedule data, tour map and calendar entries

- tour-map shortcode: Leaflet map of the tour locations with routes from the
  Congress, from the map/tours sections of data/schedule/<event>.yaml; Leaflet
  and the OSMIC, Maki and Temaki icon sets vendored; 39C3 uMap data converted.
- calendar shortcode: per tour date, a pill with an .ics download (iCalendar)
  and a Google Calendar link; Font Awesome Free vendored, fa-icon partial.
- README sections for the calendar and tour map shortcodes and the map data.

assets/vendor/fontawesome/regular/square-plus.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><!--! Font Awesome Free 7.3.1 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2026 Fonticons, Inc. --><path fill="currentColor" d="M64 80c-8.8 0-16 7.2-16 16l0 320c0 8.8 7.2 16 16 16l320 0c8.8 0 16-7.2 16-16l0-320c0-8.8-7.2-16-16-16L64 80zM0 96C0 60.7 28.7 32 64 32l320 0c35.3 0 64 28.7 64 64l0 320c0 35.3-28.7 64-64 64L64 480c-35.3 0-64-28.7-64-64L0 96zM200 344l0-64-64 0c-13.3 0-24-10.7-24-24s10.7-24 24-24l64 0 0-64c0-13.3 10.7-24 24-24s24 10.7 24 24l0 64 64 0c13.3 0 24 10.7 24 24s-10.7 24-24 24l-64 0 0 64c0 13.3-10.7 24-24 24s-24-10.7-24-24z"/></svg>