Establish versioning and other info for media files

[dlareau]

One of the biggest issues I have with the media files at the moment is that you can't tell from the hunt management page alone which files are downloaded and if your download succeeded.

This issue proposes that media files now store version and last download time information so that something like "v2 (3-20-20 07:08:10)" can be displayed next to the download buttons on the management page. This would be a great time to switch over to the "download elsewhere and copy into place" strategy at which point we could bump the version number any time we successfully download and copy in the files.

If I wanted to get really fancy with it, the versioning could just be a file suffix and then we could theoretically allow switching between versions.

[dlareau]

This needs to be rethought due to the new upload interface. Still would be nice to have some sort of versioning though.