Refactor staking system

[gabririgo]

Summary

Upgrade the staking proxy implementation in the staking system.

Motivation

The Rigoblock V3 protocol uses a new pool registry and in order to support new pools for incentives, the staking implementation requires being upgraded.

Specification

The new staking implementation should use the new registry (which is a deployment constant in the staking implementation, i.e. not upgradable) as a deployment constant.

Notes

It has been implemented.