Disk storage clean up

[ntarocco]

While it is essential to keep safe the uploaded video file and any version of it, we can safely delete generated artifacts that are not used anymore. This will decrease the disk usage.

Create a recurrent task that runs every day/week and will:

1. get all buckets (record and deposits)
2. get all ObjectVersions that are not latest and are not master file (basically frames and subformats)
3. remove the link to the file_id object

The task #1888 should do the rest to remove files from disk.