Reorg BLS module

[hwwhww]

What is wrong?

For having better key management and convenient common interface for BLS signature.

How can it be fixed

1. Move eth/utils/bls.py to py_ecc.
   • Maybe start after Library refactor py_ecc#31?
2. Implement a new BLSKeyAPI interface in eth-keys.
   • It seems the currentKeyAPI is only for ECDSA? We may add a BaseKeyAPI, and modify the current ECDSA APIs to ECDSAKeyAPI.
   • So do PublicKey, PrivateKey and Signature interfaces.
3. Refactor and optimize:
   • Routine for processing deposits py-evm#1640 (comment)

[ralexstokes]

closing this due to staleness. we can revisit if needed :)