kaiax/gov: Add gov module

[ian0371]

Proposed changes

Add governance module. Merge below PRs into dev.

• https://github.com/kaiachain/kaia/pull/93
• https://github.com/kaiachain/kaia/pull/104
• https://github.com/kaiachain/kaia/pull/113

Types of changes

• [ ] Bugfix
• [x] New feature or enhancement
• [ ] Others

Checklist

• [x] I have read the CONTRIBUTING GUIDELINES doc
• [x] I have read the CLA and signed by comment I have read the CLA Document and I hereby sign the CLA in first time contribute
• [x] Lint and unit tests pass locally with my changes ($ make test)
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)
• [ ] Any dependent changes have been merged and published in downstream modules

[ian0371]

I'll add validator-related updates in another PR.