Implement Istanbul hardfork

[MrLuit]

Todo

• Add CHAINID opcode at 0x46, which pops 0 stack arguments, and pushes the current chain ID onto the stack (256-bit value).
• Add SELFBALANCE opcode at 0x47, which pops 0 stack arguments, and pushes the balance of the current address onto the stack.

EIPs

• EIP 1344: ChainID opcode
• EIP 1884: Repricing for trie-size-dependent opcodes