R4R: Distribution Queriers & CLI query commands

[cwgoes]

Adds queriers and distribution CLI query commands for:

• Module parameters
• Outstanding (un-withdrawn) rewards
• Outstanding validator commission
• Validator slashes
• Current delegator rewards (if they were to be withdrawn)

Closes #3307
Closes #2359

• 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

---

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 #3319 into develop will decrease coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #3319      +/-   ##
===========================================
- Coverage    55.57%   55.55%   -0.03%     
===========================================
  Files          132      132              
  Lines         9528     9528              
===========================================
- Hits          5295     5293       -2     
- Misses        3898     3900       +2     
  Partials       335      335

[alexanderbez]

Tested and looks good! Just have a few remarks 👍