Add governance and policy contracts

[chenquanyu]

This PR is a code implementation of #2, #3, #5. Close #2, Close #3, Close #5.

This PR is going to add the Governance contract to manage consensus list, Policy contract to manage policy parameters. We will have the first Phase of consensus in genesis block and the users can vote for new Phases with GAS in Governance contract. The GovReward contract will keep the reward GAS for governance voters. For governance requirements, please refer to https://docs.google.com/document/d/11iDJGpCDNrKmPQN8TOhmEqBlWZAOstH15j3Afc2xoQo/edit#heading=h.idvp9uir3xt8.

The GovernanceVote contract is an abstract contract for Policy and other contracts (like GovProxyAdmin) who need a 1/2 consensus vote to execute some function.

We will use upgradable contracts for Governance, Policy and GovReward, ERC1967Proxy is used as proxy and GovProxyAdmin is used as the admin of upgrade.

For the implemention of #5, we will need following contracts in genesis alloc:

1. GovProxyAdmin 0x1212000000000000000000000000000000000000
2. Governance Proxy 0x1212000000000000000000000000000000000001
3. Governance Implemention 0x1212100000000000000000000000000000000001
4. Policy Proxy 0x1212000000000000000000000000000000000002
5. Policy implemention 0x1212100000000000000000000000000000000002
6. Governance Reward 0x1212000000000000000000000000000000000003
7. Governance Reward implemention 0x1212100000000000000000000000000000000003

[cloud8little]

https://github.com/bane-labs/go-ethereum/pull/7/files#diff-76ed074a9305c04054cdebb9e9aad2d818052b07091de1f20cad0bbac34ffb52R36
GOBIN -> GETHBIN

[nicolegys]

From the user's point of view, there is no function for users to get their voted draftIds. If someone has voted for several proposals in the past phases, he must walk through the previous transactions to find the draftIds and then get his ethers back (Unless he wrote them down somewhere by himself).

[nicolegys]

merge?

[chenquanyu]

From the user's point of view, there is no function for users to get their voted draftIds. If someone has voted for several proposals in the past phases, he must walk through the previous transactions to find the draftIds and then get his ethers back (Unless he wrote them down somewhere by himself).

May be will need a UI for users to vote, and will list all the voted draft from event log.

[AnnaShaleva]

Oh, the PR was updated, so I'm leaving existing comments here for now and continue review once my review is re-requested.

@chenquanyu, please, tag me once you finish adjustments.

[chenquanyu]

Is this fact connected with the way how we deploy system contracts? I.e. some storage items are missing in genesis allocations?

Immutable variables are evaluated once at construction time and their value is copied to all the places in the code where they are accessed. So it has nothing to do with storage, we are solving this problem by overriding these methods which use "immutable __self" variable.

[AnnaShaleva]

LGTM otherwise.

[AnnaShaleva]

@roman-khimov, @txhsl, @nicolegys, @ZhangTao1596 ready for the final review&merge.

[chenquanyu]

We have not yet added the function of burning fees. We can send part of fees to an empty address in the governance contract to burn and configure this burning ratio in the policy contract. Issue opened in #163.

[AnnaShaleva]

LGTM.

[mialbu]

Minor documentation and consistency-related comments.