Show waypoint photos from newer p4n2gpx exports

A newer p4n2gpx run (Ruby rewrite, ~/test/mapping/p4n2gpx) started
emitting one plain GPX <link href> per park4night listing photo,
which this app parsed but never displayed. Gpx.waypoint_photos
collects them into a photos property; the waypoint popup renders them
as a row of thumbnails above the description, each opening full-size
in a new tab. Absent on older exports and plain GPS waypoints, so the
row just doesn't render for those.

lib/maptool/gpx.rb

@@ -51,11 +51,21 @@ module Maptool
           "category" => child_text(wpt, "type"),
           "color" => ext[:color],
           "icon" => ext[:icon],
+          "photos" => waypoint_photos(wpt),
         },
       }
     end
     private_class_method :waypoint_feature
 
+    # <link> is plain GPX 1.1 (a wpt/trk/rte can carry any number of them),
+    # not a vendor extension like waypoint_style's <osmand:*> — a newer
+    # p4n2gpx export started emitting one per park4night listing photo. A
+    # plain GPS waypoint has none, so this is almost always empty.
+    def self.waypoint_photos(wpt)
+      wpt.get_elements("link").filter_map { |link| link.attributes["href"] }
+    end
+    private_class_method :waypoint_photos
+
     OSMAND_NAMESPACE = "https://osmand.net"
     private_constant :OSMAND_NAMESPACE