Cooperative settlement

[palango]

What this PR does

Implement cooperative settle (#1383)

Tasks

• Add check (+ test) for withdraw of to small amount (settle withdraw < deposit - withdraws)
• Fix event data, adapt tests (test_cooperative_settle_channel_event)
• Add gas estimates for cooperative settlement
• Fix event checker to be able ti handle multiple events of same kind

Why I'm making this PR

What's tricky about this PR (if any)

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• If the PR is fixing a bug or adding a feature, add an entry to CHANGELOG.md.
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  • solidityFunction
  • _solidity_argument
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  • The deployment script deploys the new contract.
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[codecov]

Codecov Report

Merging #1474 (7ddc3cb) into master (2bfc938) will increase coverage by 0.15%.
The diff coverage is 100.00%.

❗ Current head 7ddc3cb differs from pull request most recent head f605324. Consider uploading reports for the commit f605324 to get more accurate results

@@            Coverage Diff             @@
##           master    #1474      +/-   ##
==========================================
+ Coverage   80.66%   80.81%   +0.15%     
==========================================
  Files          22       22              
  Lines        1562     1564       +2     
  Branches      190      190              
==========================================
+ Hits         1260     1264       +4     
+ Misses        255      253       -2     
  Partials       47       47              

Impacted Files	Coverage Δ
raiden_contracts/utils/proofs.py	97.36% <ø> (+4.68%)	⬆️
raiden_contracts/utils/events.py	92.00% <100.00%> (+0.57%)	⬆️

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[karlb]

Really nice to finally have a coop settle after such a long time!

[andrevmatos]

I'm no solidity expert, but this looks good to me. It'd be good to have someone else more into solidity itself to review it though. I like the approach to leverage the double-withdraw signed structures, but we really need to optimise those gas usages