Migrate to Redux Toolkit

[leosuncin]

Redux toolkit is the new recommended way to work with Redux and because this is example followed by devs that use Cypress I think it would be a good idea to update the code to use it. RTK allows to write less and improve readability of code.

Thing I done:

• Switch to slice pattern, no need to define action/reducer/selectors in separate files
• Still use reselect's selectors
• Update test files when needed
• Keep the same code coverage
• Format code with prettier (--no-semi --single-quote)

Pending ones

• [x] ~Use Redux's hooks API instead of connect/map~ Require react-redux >= v7.1
• [x] Convert class components to functional components, use hooks API

[leosuncin]

Optional:

• ~Use React Testing Library for unit test, but I didn't see jest as dependency~ Remove old tests
• [ ] Upgrade React Redux to v7 and use Hook API over connect