Use KeyGenHistory contract for initialization.

[afck]

Replace the temporary config-file based initialization of the keys and key shares for hbbft with the KeyGenHistory contract.

• The script that generates the TOML file needs to generate the contract constructor bytecode instead, together with the serialized Ack and Part parameters from a simulated execution of SyncKeyGen by the initial validators.
• The engine needs to initialize itself from the genesis block, using the contract's acks and parts fields: It creates a SyncKeyGen instance and calls handle_part and then handle_ack for all those messages. Finally, SyncKeyGen::generate will create the correct NetworkInfo.