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/solid/arrow-rotate-backward.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! 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="M256 64c-56.8 0-107.9 24.7-143.1 64l47.1 0c17.7 0 32 14.3 32 32s-14.3 32-32 32L32 192c-17.7 0-32-14.3-32-32L0 32C0 14.3 14.3 0 32 0S64 14.3 64 32l0 54.7C110.9 33.6 179.5 0 256 0 397.4 0 512 114.6 512 256S397.4 512 256 512c-87 0-163.9-43.4-210.1-109.7-10.1-14.5-6.6-34.4 7.9-44.6s34.4-6.6 44.6 7.9c34.8 49.8 92.4 82.3 157.6 82.3 106 0 192-86 192-192S362 64 256 64z"/></svg>