Add `className` and `style` properties to wrappers of UI components

[arnautov-anton]

Allows users to style default components with libraries like Styled Components 💅 or Emotion.

Example with styled-components:

import styled from "styled-components";
import { Activity } from "react-activity-feed";

const CustomActivity = styled(Activity)`
  background-color: ${({ activity: { verb } }) => verb === "repost" ? "hotpink" : "white"};
  color: #ddd;
`

[github-actions[bot]]

size-limit report 📦

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
dist/index.js	217.54 KB (+0.31% 🔺)	4.4 s (+0.31% 🔺)	442 ms (-32.39% 🔽)	4.8 s
dist/index.css	8.17 KB (0%)	164 ms (0%)	0 ms (+100% 🔺)	164 ms