2.4 - PoA Consortium

Build off of current PoA implementation to support a consortium of Authority nodes, with clients requiring a threshold (e.g. 3/4 of Auth nodes) of signatures before accepting.
This implementation will require multiple Authority nodes to all agree on the ordering of transactions before signing and broadcasting to clients, which is non-trivial. One possible solution is to have the authority nodes run latency-based consensus from 2.3.