Simplify the files module (and prepare hardfork)

After #580 (closed) (embargo move) and !376 (merged), files.py can be simplified as we do not need to repack published uploads.

This has also implications for our hardfork. We have to ensure that the old raw files stay as they are. You can assume that

• The raw files do not include any POTCAR files. (#590 (closed))
• Only one of these files contains actual contents. Its either all in public or all in restricted. (#590 (closed))

Maybe we keep the old file names and instead of repacking, we simply rename them? We could also test, if the old NOMAD works with missing restricted or public files.

We should not opt for just a single file name. For operation concerns (e.g. create mirror harddisk) it would be easier if the restricted status can be determined by the file name alone.