Bug: Same file is re-download if download is restarted incase of error

[Rexadev]

When download 1500 files program get's stuck and I have to run it again for the artist that causes it to download duplicates.

Solution -

1. Before downloading create a file with URLs to download and strike off as one downloads
2. That way it would b possible to Pause/Resume an Artist's download
3. Also add a temporary extension while the file is downloading like chromium's .chrdownload

[Rexadev]

@jabbey1