v2.3: add --dump/delete-orphans

New args to dump and delete orphaned series and episodes.
Also, fix `series' slot of episode objects which don't have it
already.
v2.3.1: handle download issues gracefully

If the torrent URL was not downloaded, then the episode was wrongly
marked as downloaded.  Also, transmission-remote can return a 0 exit
status when it doesn't work, so look harder at the stdout and stderr
to glean success or failure.  Also fixed the file handler.