new: add bor consensus

Makefile

accounts/accounts.go

consensus/bor/api.go

consensus/bor/bor.go

consensus/bor/clerk.go

consensus/bor/errors.go

consensus/bor/genesis_contracts_client.go

consensus/bor/merkle.go

consensus/bor/rest.go

consensus/bor/snapshot.go

consensus/bor/snapshot_test.go

consensus/bor/span.go

consensus/bor/validator.go

consensus/bor/validator_set.go

core/types/state_data.go

eth/backend.go

eth/config.go

go.mod

go.sum

les/client.go