Update ADDRESS_DATA_SIZE to 20

[Earlz]

This updates the address size to 20. Currently there is no address type implemented which consumes more than 20 bytes, so there is no reason to have the address be larger

[xuanyan0x7c7]

witness_v0_scripthash addresses contain 32 bytes data

[Earlz]

This is true, but another address type requires 64 bytes, and some other witness address types can require a dynamic size. In the prototype right now, only the 20 byte address types are supported (pubkeyhash, scripthash, EVM, x86). I think the proper way to support the larger address types in the future will be to make the UniversalAddressABI structure support a dynamic size for the address. This requires a lot of API changes though, and so I think it can be delayed until v2 (testnet, rather than prototype) of Qtum-x86