Storage: Add validation of chunks of storage after finished sync

After two nodes have synced, they should exchange hash of chunks of signatures. These could then be validated, e.g. 10 000 signatures or 100 000 signatures at a time, sorted by the "id" field of the document. If e.g. document number 30 005 is different, it means after chunk (hash) 3, we have a difference. We could actually at that time attempt to resync only from there and not everything.