Add ValidateGenesis to staking, add more tests

[ValarDragon]

Closes #890

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.
• Wrote tests
• Updated relevant documentation (docs/) - n/a?
• Added entries in PENDING.md with issue #
• rereviewed Files changed in the github PR explorer

---

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 #2450 into develop will increase coverage by 0.14%.
The diff coverage is 94.28%.

@@             Coverage Diff             @@
##           develop    #2450      +/-   ##
===========================================
+ Coverage    59.69%   59.83%   +0.14%     
===========================================
  Files          136      136              
  Lines         8405     8440      +35     
===========================================
+ Hits          5017     5050      +33     
- Misses        3055     3056       +1     
- Partials       333      334       +1

[rigelrozanski]

cool testcase design pattern!

[cwgoes]

utACK