Disk -> Tape status

[ckoerber]

We should write a script which helps backing up files on tape using the information we already have in the database.

Objective

1. Identify which files are should be backed up in general (e.g., t-sliced source averaged FF files)
2. Identify if files are already on tape or not
3. Identify if files exist on tape
4. Prepare to move files or list missing files

Prepare to move | which is the action to follow up on?

If files are on disk but not on tape and shall be backed up they
(a) Should be added to a list
(b) Should be moved

List missing files

As a first step, we can for now track a list of missing files. It is relatively easy to check nested dependencies as well.