blockchain/stake: Cleanup various parts of the treasury code.

[davecgh]

This is rebased on #3677 and #3679.

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This reworks a significant portion of the treasury code and related tests in blockchain/stake to make it more consistent with the quality of the other consensus code throughout the code base.

It is part of a larger overall effort to bring the treasury code up to the standards used throughout the rest of the blockchain consensus code.

It consists of a series of commits to help ease the review process. Each commit is intended to be a self-contained and logically easy to follow change such that the code continues to compile and works properly at each step.

See the description of each commit for further details.

A high level overview of all changes are:

• Cleanup treasury add, treasury spend, and treasurybase check code to address things such as:
  • Several of the reported error message are incorrect
  • Most of the error message don't provide very helpful messages and reference internal names that are not visible to users
  • Inconsistent errors
  • Inconsistent variable names
  • Uses less efficient inverted logic tests
  • Various misleading and inaccurate comments
  • Some checks are not in the most logical order
• Rework tests for tx type identification, treasury spends, treasury adds, and treasurybases
  • Make them more comprehensive
  • Correct various that weren't actually testing what they claimed
  • Make them much more consistent with the other tests throughout the code base
  • Use hex to bytes for hard-coded byte slices for some of the globals instead of the much more verbose raw byte slices
  • Introduce helper functions to create the various components of the transactions
  • Start with well-formed transactions and modify them for each test instead of building them from scratch every time
  • Run all identification funcs against all of the transaction types to help ensure none of them are incorrectly detected as any other
  • Significantly improves readability and adds descriptions to make it clear for people not familiar with the code
  • Modernize the test formatting
  • Effectively add more tests overall due to cross testing
  • Correct test intending to pass stakebase but not treasury add and assert it actually passes the stakebase checks
• Remove unused commented test code
• Remove duplicate tests