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/icons/maki/slipway.svg

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg width="15" height="15" viewBox="0 0 15 15" xmlns="http://www.w3.org/2000/svg" id="slipway">
+  <path d="m2 10 12 1.495V12H2v-2Zm12-4-1 1v.583L5.196 4.332l.063-.125L6.61 2.845h.831a.35.35 0 0 0 0-.7h-.976a.352.352 0 0 0-.248.103L4.723 3.753a.371.371 0 0 0-.066.09l-.109.219L2 3c0 2-.03 3.958 2.86 4.5C6.28 7.765 13 9 13 9l2-2-1-1Z"/>
+</svg>