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/brands/sourcetree.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="M427.4 203c0-112.1-90.9-203-203-203-112.1-.2-203 90.6-203.2 202.6-.1 43 13.5 84.8 38.7 119.6s60.9 60.6 101.8 73.8l0 101.7c0 3.8 1.5 7.4 4.2 10.1s6.3 4.2 10.1 4.2l96.4 0c3.8 0 7.4-1.5 10.1-4.2s4.2-6.3 4.2-10.1l0-101.6c40.8-13.2 76.5-39 101.7-73.7s38.9-76.5 39-119.4zm-271.6 0c0-90.8 137.3-90.8 137.3 0-.1 89.9-137.3 91-137.3 0z"/></svg>