R4R: Ensure Legacy Validator Delegation Invariants

[rigelrozanski]

Recreation of PR #2176 After Reverted Merge
Need to merge in develop and fix errors

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• Add Delegation to ValidatorSet type. The motivation was to be able to determine
  if a validator has a self-delegation in the unjail message handler.
  • Note, the keeper implementing the ValidatorSet interface already has Delegation defined.
• Update handleMsgUnjail to not allow a validator to unjail itself if it has no
  self-bonded delegation (it may have other delegated power).
• Update handleMsgDelegate to allow a validator to self-bond when jailed.
• Added unit tests to ensure the following:

When a validator removes it's final self-bonded share:

• the validator is jailed (existing behavior)
• delegators cannot delegate to said validator
• the validator CAN self-delegate to itself
• validator cannot unjail themselves UNLESS they have self self-bonded
• after self-bonding and unjailing themselves - the validator should be able to accept delegations again

closes: #1883

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• 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.

• 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)

[alexanderbez]

Thank you @rigelrozanski! Will address this today 👍

[codecov]

Codecov Report

Merging #2198 into develop will increase coverage by 0.04%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop    #2198      +/-   ##
===========================================
+ Coverage    63.51%   63.55%   +0.04%     
===========================================
  Files          136      136              
  Lines         8370     8380      +10     
===========================================
+ Hits          5316     5326      +10     
  Misses        2692     2692              
  Partials       362      362

[alexanderbez]

@rigelrozanski updated + fixed! Thanks again.

[rigelrozanski]

Oh dope! - if you want to approve this PR I'll merge in

[alexanderbez]

Tested ACK 👍