Fetch metadata again after download task times out

[tcely]

For #188, and other "disappearing formats" problems, it would be great if the metadata was pulled again by the software instead of the user skipping/unskipping media items.

I think we should be careful to preserve the existing metadata during this process because the video might have been deleted, and I want to still have the metadata in those cases.

[meeb]

A simple hack for this might be a timed task that scans for "is downloadable = false" media items updated 12 hours or so hours ago and deletes then re-queues metadata collection for it. This would also need a retry counter to prevent endlessly retrying undownloadable media.

[tcely]

I was thinking about a refresh_formats task that is scheduled after we complain about the file not being where we expected.

We would have to not schedule a lot of those, but it should be fine if it happens to run after a successful download too.

[meeb]

A reasonable idea, likely it might need both. That wouldn't catch, for example, private members videos which have no format matches but are then made public later as the download would never be attempted and not trigger a metadata refresh.

[tcely]

It seems like when can_download==False and there is metadata we should also schedule a refresh_formats task.