This change adds dedicated methods on metabase.Pieces to be able to add, remove pieces and also to check duplicates.
Change-Id: I21aaeff40c017c2ebe1cc85a864ae546754769cc
metabase has become a central concept and it's more suitable for it to
be directly nested under satellite rather than being part of metainfo.
metainfo is going to be the "endpoint" logic for handling requests.
Change-Id: I53770d6761ac1e9a1283b5aa68f471b21e784198
