Improve ESLint

[Chnapy]

Add/change lint rules:

• error - may affect the runtime, should break CI
  • floating promises
  • use of setTimeout/clearTimeout instead of custom promise-based timer
  • (jest) avoid .only()
  • (jest) avoid tests with same names
• warning - code quality only, should pass CI with warnings (consider using a tool like DangerJS)
  • semicolon absences
  • use type instead of interface
  • filename dash-case (Rename all files to be dash-case #29) using a plugin if necessary

Also consider using a preset (airbnb, react, ...).