Move to React

[versusbassz]

To do after #6 (upd: done)

Subtasks

• [x] Use real data from DB
• [x] state management (React.Context ???) --- IMO, it isn't necessary for now, coz the widget is too small and independent + it doesn't have too much sub-components
• [x] search for react-libraries to replace the current jquery-like ones
  • js-cookie library stays installed via npm
  • stupidtable removed
• [x] wrapping layout for entities that don't support Metabox API

Notes

• https://reactjs.org/docs/create-a-new-react-app.html#creating-a-toolchain-from-scratch
• g: react trigger render from outside
  • https://stackoverflow.com/questions/31856712/update-component-state-from-outside-react-on-server-response
• https://developer.mozilla.org/en-US/docs/Web/API/Window/DOMContentLoaded_event

[versusbassz]

I think, it's done.