[Refactoring] A global empty hash variables

[hyunsooda]

Is your request related to a problem? Please describe.
There are so many scattered literal strings of empty hash in the existing Kaia codebase and following PRs in the future.

• Empty code hash
• Empty root hash

Describe the solution you'd like
Refactoring.
We can define a types package and reuse it.

Describe alternatives you've considered

Additional context
If you look fine with this refactoring, let me proceed with it

[blukat29]

Nice spot. We could do something like https://github.com/ethereum/go-ethereum/blob/master/core/types/hashes.go

[blukat29]

There are other similar variables https://github.com/kaiachain/kaia/blob/dev/blockchain/types/derivesha/derive_sha_test.go.
We could name them like EmptyTxRootSimple. Same 0x56 and 0xc5 values, but different usages under different names.