Store validator list in the states

[sgkim126]

And changes the way to calculate the order of the block proposer.

[sgkim126]

Hi @majecty, @foriequal0 and @kseo,
Let me propose the method to decide the order of block proposer.
The previous way has two problems.

The first is the block generation should wait a long time if the validator who has been delegated lot's of stake has stopped.
It's because one node can be a generator in consecutive rounds.

The second problem is that it's not easy to calculate the block author.
Our implementation doesn't know the consensus view when closing the block.
It's because CodeChain supports PoW as well as Tendermint; the view is in the seal, but the seal is attached to the block after closing.

The new way has a simpler approach to decide the proposer but it has better property.

Briefly speaking, the order of validators is determined in the same height by considering delegation, generated blocks and round.
The validator is round-robin when the view increased.
It makes there are no stall even the node which has been delegated lots of stakes has stopped; still, the strong validator has more chance to generate the block.
Moreover, it's very easy to implement in our implementation because they are easily calculated from the states of the parent block and the block author.

[majecty]

LGTM

[sgkim126]

I resolved the conflicts with #1597

[sgkim126]

@foriequal0 The only change after you approved is resolving conflicts. I'll merge it.