R4R: Simulate from a genesis file

[cwgoes]

Closes #3182

Includes new Makefile commands test_sim_gaia_custom_genesis_fast and test_sim_gaia_custom_genesis_multi_seed, which both default to using ~/.gaiad/config/genesis.json.

To test with the gaia-10k genesis, download this file to ~/.gaiad/config/genesis.json and run one of those new commands.

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.
• Wrote tests
• Updated relevant documentation (docs/)
• Added entries in PENDING.md with issue #
• rereviewed 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 pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #3428 into develop will decrease coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #3428      +/-   ##
===========================================
- Coverage    59.36%   59.34%   -0.03%     
===========================================
  Files          134      134              
  Lines         9972     9972              
===========================================
- Hits          5920     5918       -2     
- Misses        3679     3681       +2     
  Partials       373      373

[rigelrozanski]

Looks good - few comments to address within