Develop protocol staking adapter

[gabririgo]

Summary

Connect the protocol to the GRG staking system.

Motivation

Smart pools that have their own stake require an adapter to communicate with the staking system.

Specification

The adapter should allow the pool to stake to itself.
A "stake" method will be implemented which will batch in one transaction:

1. Set allowance to GRG transfer proxy
2. stake and deposit to GRG vault
3. delegate stake to self.
   An "undelegateStake" and "unstake" methods will be implemented as well to allow the pool to withdraw its own stake.
   A "withdrawDelegatorRewards" method will be developed to allow the pool to withdraw delegator staking rewards while staking.

Notes

It has been implemented.