Upload date no longer written to tags

[carrnax]

Previously when downloading tracks, the upload date was written to the Date tag in the format YYYY-MM-DD[T]HH (i.e. 2015-12-17T17), but this is no longer the case. The --addtimestamp argument simply adds a unix timestamp of the most recent edit to the upload onto the beginning of the track's filename, rather than adding the original upload date, so this is not a proper workaround.