changes to download manager

Still having had problems to sync files with ftp servers, I decided to change the downloader plugin as you already may have seen at the xp11 page. The next days I will change all other files.

Downloads per continents are now grouped together (Forests, w2xp sceneries, w2xp sceneries net).

Even if the date assumes these files are new, there aren’t and there’s no need to download files again. The latest uploads were the Forests and VFR-Landmarks sceneries uploaded October 28.