Update SyncedPoint to use leveldb

[jacque006]

Problem

When a node starts syncing when the client process starts up, it will sync from the genesis block defined in genesis.json. However, various StorageEngines and other components could be up to date on disk. This full re-syncing is unnecessary and makes node restarts/crashes slower to recover from.

Solution

• Update SyncedPoint (SP) to use leveldb to properly store SP data.
• Use SP data (if found) to begin syncing from the last block/batch stored when syncer starts its initial sync.

Consider

This may need to be implemented after we have persisted batch and transaction storage