[GIP-67] Changes to GIP-63 & CRV

Motivation

The DAO already voted for listing Curve V2 farms in GIP-63 (see https://snapshot.org/#/gearbox.eth/proposal/0x29db5080123fae3e46b6f5b0b82d7c2bce3ca81ffa39f31db709d28aac0ea050). These changes have not taken effect, but some of the contracts have already been deployed. After the CRV hack, it's obvious that some system parameters should be updated. This propozal assumes to roll back some changes / change some elements of the system.

Note: All funds are SAFU. The required changes are about maintaining the protocol and are not related to the elimination of potential attack vectors. This proposal is an improvement before the product goes live.

Specification

• set ZeroPriceFeed for crvETH and all related assets
• set LT = 0 for crvETH token as well as Convex crvETH LP token and staking position
• set LT for CRV, FXS, CVX tokens as 0 for all existing credit managers

The main use case of holding CRV/FXS/CVX tokens on Credit Accounts is just as Farming Rewards. So changing Liquidation Thresholds for them will not change the user experience at all, while it improves protocol's robustness. No user would get liquidated and lose assets as a result of this vote.