Refactor Distributed Key Generation

The implementation of the distributed key generation scheme which is currently placed in [CommitteeMember](https://github.com/input-output-hk/TreasuryCoin/blob/dev/examples/src/main/scala/examples/hybrid/state/CommitteeMember.scala) (and DistrKeyGen class it treasury-crypto) probably needs to be reworked. There are a lot of unnecessary, complex code.
First of all it should not hold private keys of committee members and probably it is a good idea to integrate this functionality completely into the TreasuryState.

An investigation on the better architechture is needed