Refactor Evidence Age Util + Governable Consensus Params

[alexanderbez]

Description

• Remove usage and dependency of the main store key.
  • Load(Latest)Version no longer requires a store key parameter.
• Add ParamStore to the BaseApp. The ParamStore is a simple interface that the x/params module subspace type implements. This will allow consensus parameters to be modified via governance.
• Add checkType call to Subspace#GetIfExists.
• Remove x/evidence params

The only potentially contentious change here is the change to BaseApp and its use of the param store provided by x/params. Note, however, BaseApp does not rely on that package.

TODO:

• Update any necessary baseapp docs
• Test on a localnet
• Handle state export?

closes: #5532

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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 #5952 into master will increase coverage by 0.00%.
The diff coverage is 57.28%.

@@           Coverage Diff           @@
##           master    #5952   +/-   ##
=======================================
  Coverage   58.27%   58.28%           
=======================================
  Files         396      397    +1     
  Lines       23595    23646   +51     
=======================================
+ Hits        13750    13782   +32     
- Misses       8883     8902   +19     
  Partials      962      962           

[alexanderbez]

This is the core change with regard to the initial intent of the PR.

/cc @cwgoes @ebuchman @melekes