Chore: Design comments

[roxdanila]

Context

Fixes part of the items in #324

Changes proposed in this pull request

• Use getEthForAsset in MCR. To avoid reimplementing existing logic, the calculations at MCR.sol#L104 should be replaced with priceFeed.getEthForAsset(...):
• Use Math.min: The ternary expression at Pool.sol#L644 can be replaced with Math.min to improve readability.
• Spelling and grammatical errors:
  • Governance.sol#L463: totalRewar -> totalReward
  • Cover.sol#L648: initialProuctTypesCount -> initialProductTypesCount
• Unused SafeMath: The SafeMath library is included at Governance.sol#L15 but none of its functions are used and thus it can be removed. This is actually used in multiple places (see .add() occurrences)

Test plan

Made sure existing tests run.

Checklist

• Rebased the base branch
• Attached corresponding Github issue
• Prefixed the name with the type of change (i.e. feat, chore, test)
• Performed a self-review of my own code
• Followed the style guidelines of this project
• Made corresponding changes to the documentation
• Didn't generate new warnings
• Didn't generate failures on existing tests
• Added tests that prove my fix is effective or that my feature works

Review

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