Eth2.0-specs: SSZ: Add `bytesNN` and remove `Address`

[hwwhww]

• Add bytesNN
  
  
  
  • BLS points:
    
    
    
    
    
    • Per https://github.com/ethereum/eth2.0-specs/blob/c1a3b29145c84c6ac4422314b7b54898ac9f6693/specs/core/0_beacon-chain.md, it looks nice to use bytes48 for the G1, G2 points (option 5).
    
    
    
  
  
  • StatusFlags:
    
    
    
    
    
    • the current ValidatorRecord.status_flags: uint64 could also benefit from it. -> bytes8 (edited)
    
    
    
  
  
  • (TBD) Replace hash32 with bytes32.
  
  
• Remove Address: it's unused.

[djrtwo]

the current ValidatorRecord.status_flags: uint64 could also benefit from it. -> bytes64

note: that uint64 is bytes8.

Also, I think it might generally be easier to bitwise manipulate integers in python rather than byte arrays. I don't feel very strongly, but @vbuterin made that argument here https://github.com/ethereum/eth2.0-specs/issues/371#issuecomment-450497143

[JustinDrake]

• +1 for removing hash32 (in favour of bytes32).
• Similarly remove hashN (in favour of bytesN).