Implement modified Haven VSS

[joebebel]

Setting aside performance, initially, the modified Haven VSS needs to be fully implemented feature wise. The three primary changes from the Haven paper are:

1. Using a weighted scheme, as described in the draft design proposal, aggregating all shares belonging to the same node into the same send/echo/ready messages.
2. Evaluating polynomials at omega^i instead of i. This can be done the simple way for now and FFT optimizations can be added later.
3. Implementing vector commitment as Merkle tree (or deciding that some other vector commitment scheme is superior)

Implementing the VSS to feature-completeness will allow the performance tweaking to happen in parallel to building the rest of the protocol.

[joebebel]

Never mind, we're going with an on-chain approach for now.