Refactor Distributed Key Generation

[dkaidalov]

The implementation of the distributed key generation scheme which is currently placed in CommitteeMember (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