Change staking cool down to 60 days

Motivation for change

The current cool down period for staking SX is 14 days. A number of people in the community have reached out and told us that they think that 14 days is too low of a time period and want to increase it substantially to 30-90 days, especially given the overall weak crypto market at the moment. Many projects have year-long staking periods, such as Curve for example (4 year vesting period on staking rewards). SX staking rewards are meant to reward long-term SX holders that participate in governance; changing the staking cool down period to 60 days will help to further align that.