Add state management, context (v1.4)

[OleksiyRudenko]

Contexts:

• unit switch
• data

[OleksiyRudenko]

Extra materials:

• https://daveceddia.com/react-state-management/
• https://blog.isquaredsoftware.com/2021/01/context-redux-differences/
• https://www.reddit.com/r/reactjs/comments/hhc7lq/its_a_shame_mobx_never_got_recognitionadoption/?utm_medium=android_app&utm_source=share

Not so popular state managers:

• https://github.com/pmndrs/zustand
• https://mobx.js.org/README.html
• https://recoiljs.org/
• https://github.com/pmndrs/valtio