cmd, consensus/ethash, eth: miner push notifications

cmd/geth/main.go

cmd/geth/usage.go

cmd/utils/flags.go

consensus/ethash/algorithm_test.go

consensus/ethash/consensus.go

consensus/ethash/ethash.go

consensus/ethash/ethash_test.go

consensus/ethash/sealer.go

consensus/ethash/sealer_test.go

eth/backend.go

eth/config.go

les/backend.go