Use uint256 for account balance (#580)

accounts/abi/bind/backends/simulated.go

accounts/abi/bind/backends/simulated_test.go

cmd/evm/runner.go

cmd/geth/retesteth.go

cmd/puppeth/genesis.go

cmd/restapi/apis/accounts_api.go

cmd/state/stateless/state.go

common/big.go

common/types.go

consensus/ethash/consensus.go

consensus/misc/dao.go

core/blockchain_test.go

core/evm.go

core/genesis.go

core/state/database_test.go

core/state/dump.go

core/state/history_test.go

core/state/intra_block_state.go

core/state/intra_block_state_test.go

core/state/journal.go