Gaia upgrade demo

[ethanfrey]

Supporting documentation for cosmos/cosmos-sdk#4233

This includes integration of the upgrade module in gaia, and a simple walk-through to validate all client commands on operational processed for doing in-place upgrades: https://github.com/regen-network/gaia/blob/gaia-upgrade-demo/docs/upgrade-demo.md

Please try it out to fully understand the upgrade module. This can also be merged if desired, but current state is meant to demo.

• Targeted PR against correct branch (see CONTRIBUTING.md)

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md

• Reviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge PR #XYZ: [title]" (coding standards)

[fedekunze]

merging this to fedekunze/upgrade-module. I'll push the fixes there directly as I don't want to take more of your time. Thanks @ethanfrey