Chain log with all protocol deployments

[PaulRBerg]

Problem

While working on the proxy plugin, we stumbled upon the issue described in #36.

Thinking about a solution, I have discovered another problem - that we offer zero on-chain support to integrators in terms of the ability to fetch the Sablier V2 contract addresses in another smart contract.

Solution

To address this problem, as well as fix #36, we should build something similar to Maker's ChainLog contract. The documentation for Maker's contract can be found here.

[PaulRBerg]

A couple of thoughts on this:

• I ended up implementing a simple registry in feat: plugin and chain log #38, as I did not think it worthwhile to replicate the complexity of Maker's versioning system given our current needs. We may consider adding an unlist function to the registry.
• We should ask future users if they would find it valuable to have a versioned on-chain registry.
• To implement a versioned similar to Maker's, we would need a storage pattern similar to what Rob Hitched called "Mapped Structs with Delete-enabled Index", which he implemented in his library UnorderedKeySet. This library is not up-to-date with the latest version of Solidity, though.