Implement BrPage component

In the SPA code, this component should look something like:

import { BrPage, TYPE_CONTANER_BOX } from '@bloomreach/react-spa-sdk';

function App() {
  return (
    <BrPage configuration={configuration} mapping={{ News: NewsComponent, [TYPE_CONTANER_BOX]: MainComponent }}>
      <header>
        <BrComponent path="header" />
        <nav>
          <BrComponent path="menu" />
        </nav>
      </header>
      <section>
        <nav class="sidenav">
          <BrComponent path="sidebar" />
        </nav>
        <div class="container">
          <BrComponent>
        </div>
      </section>
      <footer>
        <BrComponent path="footer">
      </footer>
    </BrPage>
  );
}

Requirements:

• Pass the configuration object as-is so we can refer to the documentation of the Shared SDK (and don't change the code if new options are being introduced).
• This should be mostly a wrapper around `initialize` call from the shared SDK.
• Use React's context API to pass the page model to BrComponent.
• Implement serialization and deserialization (hydrate) of the page model to support SSR.
• Implement HTML-comments rendering as a React component so we can reuse that internally later:

    return (
      <>
        { this.props.model.getMeta()
            .filter(meta => META_POSITION_BEGIN === meta.getPosition())
            .map(meta => <Meta meta={meta} />)
        }
      </>
    );