R4R: Staking Spec Upgrade

[rigelrozanski]

• general minor reorg of spec folder
• switch staking spec to remove pseudo code and only accurately and concisely describes the objectives of the code
• other minor things:
  • some missing json struct tags for MsgCreateValidator where updated
  • missing ensure length was added to handleMsgCreateValidator

closes #1268

followup issues:
#3324
#3325
#3326

• 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)

[jackzampolin]

Left some comments ☝️ I think we need some more explaination in a couple of the sections noted. Also maybe we should break the LooseTokens -> NotBondedTokens stuff out to another PR?

[cwgoes]

First pass. I think this spec is definitely more useful than the current pseudocode, but I would also like to see a more abstract "staking model" spec outlining the formal properties we're trying to provide (e.g., lying to a lite client is always a slashable offense). That doesn't need to happen in this PR.

[cwgoes]

A few more minor suggestions - once addressed/applied LGTM.