Fix validator power decrease bug

[cwgoes]

• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Updated CHANGELOG.md
• Updated Gaia/Examples
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)
• Added appropriate labels to PR (ex. wip, ready-for-review, docs)

[rigelrozanski]

Are no updates sent back to Tendermint at all in this circumstance? i.e. does it create a change but just not the correct one?

[cwgoes]

Are no updates sent back to Tendermint at all in this circumstance? i.e. does it create a change but just not the correct one?

No updates are sent back - as demonstrated in the testcase, and just reading through the logic in UpdateValidator, we set the Tendermint update key if (a) the validator's power is increasing (still bonded), (b) the validator switches from unbonded to bonded, or (c) the validator switches from bonded to unbonded - but if the validator stays bonded but decreases in power, we don't set any Tendermint update at all.

[codecov]

Codecov Report

Merging #1566 into develop will increase coverage by 0.02%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop    #1566      +/-   ##
===========================================
+ Coverage    64.07%   64.09%   +0.02%     
===========================================
  Files          122      122              
  Lines         6666     6670       +4     
===========================================
+ Hits          4271     4275       +4     
  Misses        2148     2148              
  Partials       247      247

[cwgoes]

Ready for review.

I think we should try to simplify the maze of conditionals in UpdateBondedValidators in a future PR, perhaps using case statements or separating the iteration / store update steps more cleanly.

[rigelrozanski]

Totally agree that this is a great place for case statements to make more clear - opened an issue #1584

[rigelrozanski]

Simple enough changes! Thanks!