Historical Beacon RNG

[jaybuidl]

Adapted from @kevincharm's RandaoAccessor

Specifications

https://docs.google.com/document/d/1hKlzk51z-ULnfSL4sQ7aCl70IQBxObtr1i8ZfsYl6MY/edit

Usage

1. Court is in Staking phase. The bot calls passPhase(), which makes the RNG emit a Request(_blockNumber) event,
2. Court is now in Generating phase. The bot listens to the Request event and retrieves the requested block number, then retrieves the block header from RPC with the eth_getblockbynumber method, then RLP-encodes the header using getBlockWithRLP(), finally provides the header to the RNG by calling verifyRecent(),
3. The bot calls passPhase(), the Court is now in Drawing phase.