Change strings to []byte

[cubismic]

Current implementation uses string a lot to follow the types of codechain-rpc-js, codechain-primitives-js.

But Golang encourages to use byte slice rather than string for many reasons.

So most of the string types in this repository should be changed to []byte

[cubismic]

These files contain functions that gets or returns string

• [ ] account.go
• [ ] base.go
• [ ] chain.go
• [ ] types.go
• [ ] primitives
  • [ ] bignumber.go
  • [ ] hexstring.go
• [ ] crypto
  • [ ] hash.go
  • [ ] bech32.go

[majecty]

@gurrpi You can try this issue.

[baumstern]

@gurrpi You can try this issue.

@majecty Thanks for your considering. I'll take care of this. :)