Rewrite developer (account) specific code about picotorrent

[saul]

Also see SHGetKnownFolderPath - call it with FOLDERID_Downloads.

[vktr]

@d-kr, @saul

Hi, thanks! Fortunately, that file (along with the header) is not in use. They are artifacts from an old proof-of-concept.

Here's the current main window, https://github.com/picotorrent/picotorrent/blob/develop/src/ui/main_window.cpp

And here's the relevant part in the new code, https://github.com/picotorrent/picotorrent/blob/develop/src/app/controllers/add_torrent_controller.cpp#L58

Thanks for reporting, I'll remove the file :)