Fund Community Pool -- Part II

[alexanderbez]

A continuation of #5249 that performs some cleanup, addressing some unresolved comments and supporting simulation for the new message type.

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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)

[codecov]

Codecov Report

Merging #5384 into master will decrease coverage by 0.02%.
The diff coverage is 25%.

@@            Coverage Diff             @@
##           master    #5384      +/-   ##
==========================================
- Coverage   54.51%   54.48%   -0.03%     
==========================================
  Files         311      311              
  Lines       18719    18721       +2     
==========================================
- Hits        10205    10201       -4     
- Misses       7736     7742       +6     
  Partials      778      778

Impacted Files	Coverage Δ
x/distribution/handler.go	7.14% <0%> (ø)	⬆️
x/distribution/client/cli/tx.go	4.7% <0%> (-0.06%)	⬇️
x/distribution/keeper/keeper.go	82.71% <100%> (ø)	⬆️
x/distribution/types/msg.go	56.92% <42.85%> (ø)	⬆️
x/mock/app.go	62.83% <0%> (-2.71%)	⬇️