New proxy design: VTable / Diamond / Router proxy

[Amxx]

🧐 Motivation
The current proxy designs (transparent proxy & diamond proxy) offer great upgradability mechanism, but fail to address some of the issues which are usually addressed through proxies, such as circumventing the contract size limit.

📝 Details
Add one or mutiple proxy design that redirects calls depending on the msg.sig.

[frangio]

There is a relevant conversation going on in the Solidity Forum.

[mudgen]

I suggest that we move ahead with a diamond implementation. I made this issue: #2793