[ref] databases : use generic backend everywhere

blockchain/apply_valid_block.rs

blockchain/check_and_apply_block.rs

blockchain/dbex.rs

blockchain/lib.rs

blockchain/revert_block.rs

blockchain/sync.rs

conf/lib.rs

core/lib.rs

crypto/lib.rs

dal/balance.rs

dal/block.rs

dal/certs.rs

dal/currency_params.rs

dal/identity.rs

dal/lib.rs

dal/writers/block.rs

dal/writers/certification.rs

dal/writers/dividend.rs

dal/writers/identity.rs

dal/writers/requests.rs