Refactoring React code of Theme

[sonufrienko]

We can improve speed of rendering.

Todo:

1. replace index to *.id where we can
2. remove computing from render() method
3. use PureComponent where we can
4. replace

onClick={() => {...}} 

with

onClick(this.handleClick)

5. Use setState callback. Replace

this.setState({ total: this.state.total + 1 });

with

this.setState((prevState) => ({ total: prevState.total + 1