Draft: [enh] import data from Duniter 1.8 leveldb database
Import data from Duniter 1.8 leveldb database. See #2.
Add adapters to get data from leveldb indexes:
- blocks
- certifications
- identities
- memberships
- wallets
- ud_value
Script is now a little faster, because we don't load the entire .json files anymore, we just iterate on leveldb indexes.