consolidated downloads dir, nextcloud origin, upload route and chat timestamps; added webdav path tests

lib/model/endpoint_data.dart

@@ -5,6 +5,9 @@ class Endpoint {
   Endpoint({required this.domain, this.path = ''});
 
   String full() => domain + path;
+
+  /// `https://` + [full], without a trailing slash.
+  String origin() => 'https://${full()}';
 }
 
 class EndpointData {