* soft-deleted files will have ObjectVersions that don't have an
  associated FileInstance

* it seems that during deletion of drafts, the references to those files
  are deleted from the DB, but the files are still kept on disk
* thus, we now consider files to be orphaned that are still present in
  the file system, but don't have entries in the database anymore

* apply Black formatting
* use plural for sub-commands, for consistency
* fix convert_to_recid() to always fetch the first PID of type 'recid'
* add command to reindex all (or some) records
* update method for instantiating RecordServices: allow the configuration
  of a factory function that creates a RecordService as desired
  (default: fetches services from current_rdm_records)

* add command for listing soft-deleted files
* add command for listing all files of a record