Allow changing vote target in Governance contract #165
Description
Rationale
Current Governance requires 2 steps to change votes from one candidate to another, which needs 2 transactions and twice wallet interactions.
- Revoke votes from current candidate, and withdraw the stake;
- Vote to another candidate and stake again.
It can be simplified to improve user experience.
Implementation
Add a method like changeVote(address candidateTo) to allow flexible adjustment on vote target.