Look for better BN128 implementation

[mkalinin]

Preamble

EthereumJ uses a custom implementation of BN128 logic. Since it was introduced an year ago different parties have made a good progress in both optimization and implementation of libraries that provides same functionality.

To Do

EthereumJ implementation needs to be benchmarked and compared with other java implementation, like https://github.com/apache/incubator-milagro-crypto (maybe this is the only one thing worth to be checked).

Benchmarks done by other clients:

• BN128: https://gist.github.com/pdyraga/4649b74436940a01e8221d85e80bfeef
• BN256, BLS12-381: https://docs.google.com/spreadsheets/d/1Z55ra7TKw-K5-Qa-bWqD4YLfccamnSuLpGNhAhp7jRI/edit#gid=1364826426