(Optional) Method in Checkpoint actor to check for quorum and emit signature

[aakoshh]

This method is an optional way for timing when the quorum even is emitted. The thinking is that we want to make the quorum as big as possible, so we don't want to emit the event as soon as quorum is reached and freeze it there. My first thought was maybe to call a method at the end of the block, although that's not a big delay.

But as explained in #205 it makes even more sense to keep accumulating signatures and let the relayers decide when they send it, because they can modify the list of signatures anyway, it's malleable. We can offer more rewards for relaying with more signatures.

[dnkolegov]

In consensus-shipyard/ipc-solidity-actors#202 the following is implemented:
QuorumWeightUpdated event is emitted every time a new signature is added after reaching the threshold weight.

[dnkolegov]

@aakoshh may we close it? Is it implemented as intended or not?

[aakoshh]

Yes, I think we can close it.