feat(Escrow): add contract

[unknownunknown1]

Initially I planned to base this contract on the newest version of Escrow but ultimately switched it to the earliest version that we also have deployed https://github.com/kleros/kleros-interaction/blob/master/contracts/standard/arbitration/MultipleArbitrableTransaction.sol
The newest version had some additional features (settlement proposal, platform fees) and gas optimizations that added complexity so I had to remove those.
Also note that this is the most basic version of escrow that uses native currency as payment. There is also another version that uses tokens instead.

---

PR-Codex overview

This PR introduces the Escrow contract, which is a multiple arbitrable transaction contract compatible with V2.

Detailed summary:

• Added the Escrow contract.
• Added enums and structs for parties, status, and resolution.
• Added storage variables.
• Added events for payment, fee payment, and transaction creation/resolution.
• Added function modifiers.
• Added constructor and governance functions.
• Added state modifiers for creating transactions, making payments, and executing transactions.
• Added functions for paying arbitration fees.
• Added comments for clarity.

The following files were skipped due to too many changes: contracts/src/arbitration/arbitrables/Escrow.sol

✨ Ask PR-Codex anything about this PR by commenting with /codex {your question}

[netlify]

✅ Deploy Preview for kleros-v2 ready!

Name	Link
🔨 Latest commit	721ab5c
🔍 Latest deploy log	https://app.netlify.com/sites/kleros-v2/deploys/6571c99d5539d50008235146
😎 Deploy Preview	https://deploy-preview-1330--kleros-v2.netlify.app/
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[codeclimate]

Code Climate has analyzed commit 721ab5c and detected 0 issues on this pull request.

View more on Code Climate.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information