Merge x/supply into x/bank

[alexanderbez]

Description

• Merge x/supply into x/bank
• Module accounts should most likely now live in x/auth, but that should be completed in a follow up PR.

As for reviewing this PR, no critical business logic or state-machine changes were made. Types and APIs were simply moved.

closes: #5913

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For contributor use:

• 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.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[fedekunze]

utACK

[jgimeno]

utACK