Update & Clarify Rewards Period

Background

DG Governance and ETH-$DG LP rewards period are 5 weeks and require a vote each time to update the rates including extending the current rates.

Proposal

Once we complete the token split, (1) Make rewards periods for New DG 2 weeks, and (2) If another proposal isn't made to update them, rewards refresh/continue at the current rate.

Rationale

Part (1) allows us to be more dynamic with updating rates while Part (2) means we're not flooded with constant "extend rewards" proposals.