fix(offchain-voting): remove duplicate checks; set node index to start from 1; tests

[fforbeck]

Proposed Changes

• Removed _verifyNode redundant check from OffchainVoting.sol
• Executing the isReadyToSubmitResult check for every new vote result
• Removed checkMemberCount from OffchainVotingHelper.sol and OffchainVoting.submitResult because this check is already done via getBadNodeError.INDEX_OUT_OF_BOUNDS.
• Fixed challengeMissingStep - missing the ACLs to submit the proposals and jail members.
• Improved revert messages.
• Refactor to consider the node.index starting from 1 instead of 0.
• Improved the test coverage for the offchain voting contracts.

[codecov[bot]]

Codecov Report

Merging #534 (fd3285f) into master (2f70d3d) will increase coverage by 5.13%. The diff coverage is 100.00%.

:exclamation: Current head fd3285f differs from pull request most recent head 0292f7e. Consider uploading reports for the commit 0292f7e to get more accurate results

@@            Coverage Diff             @@
##           master     #534      +/-   ##
==========================================
+ Coverage   85.59%   90.72%   +5.13%     
==========================================
  Files          52       52              
  Lines        1867     1866       -1     
  Branches      438      438              
==========================================
+ Hits         1598     1693      +95     
+ Misses        269      173      -96     

Impacted Files	Coverage Δ
contracts/adapters/voting/OffchainVoting.sol	95.13% <100.00%> (+53.88%)	:arrow_up:
contracts/adapters/voting/OffchainVotingHash.sol	77.27% <100.00%> (+28.43%)	:arrow_up:
contracts/helpers/OffchainVotingHelper.sol	82.53% <100.00%> (+9.81%)	:arrow_up:

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