Prop 120: Gravity Slashing Window Param Change

After the upgrade, we have observed an effect where an orchestrator that was not running during the signing phase of a gravity event will be unable to sign it after it has completed on Ethereum and been observed by a consensus of oracles, resulting in the validator being jailed at the end of the slashing window. This will require a fix in the gravity module, so until then we are increasing the ConfirmedOutgoingTxWindow to be a relatively recent block height, which will effectively prevent it from evaluating slashing events for a very long time for now.