[Tracking] Fast sync protocol

[ferranbt]

Syncer has to sync the ethereum state. Following fast mode algorithms, pick a pivot point and download recursively from that root. It would be necessary to get an approximate equation of the total number of nodes to download per block. Thus, it would be possible to estimate an approximate download time for the total state. The scheduler could split the download bandwidth between headers data (header, body and receipts) and state. By modifying this quotas is possible to control the total time to sync the blockchain.