Virgo lfn2pfn and permissions
As discussed, this PR contains:
- the lfn2pfn algorithm used by virgo (virgo_stashcache) in lfn2pfn.py
- the permission policy used by Virgo in permission.py. The 'publisher' role is introduced, that allows publisher accounts to write into scopes owned by others. In the generic permission schema, this is only possible for admin accounts.
- the original ligo permission is saved in permission-ligo.py