- attachment must have unique filename+extention
- attachments can have same (type, kind, state)

- instead of string 'flavor'
- dict() syntax does not allow using variable as keys, {} does

- works on #15

- works on #15

- reduce duplicated code

- essential lines in core.Core.put() are still commented

- the collection contains information about all sites, including local
  site, not just remote sites.