Implement even proposer selection policy

[aidan-kwon]

As an item of Kore hardfork, we modified WeightedRandom proposer selection algorithm to set zero weight from all nodes. This change minimized the effect of the change and help to stabilize the code, but it makes difference between the policy name and actual behavior.

So, we need to implement a new proposer selection policy instead of using the modified WeightedRandom.

[exalate-issue-sync]

Exalate commented: Issue Created by: aidan-kwon