Render meta-data for CMS in component rendering response to indicate head contributions

The new channel manager does many component rendering calls to re-render components and containers in a page. However, components may add scripts and styling in head contributions that need to be loaded/executed before the component works. An example is a 'Carousel' component that needs certain JavaScript and CSS to work.

When such a 'rich' component is added to a container on a page it does not work in the new channel manager. That's because it only reloads the container the component was added to via a component rendering call, and not the whole page, so the head contributions required by the new component are never rendered.

To fix this, a component rendering by the Channel Manager should include meta-data (preferably as JSON inside an HTML comment, like the other meta-data for components and containers). That meta-data should indicate that the rendered markup also contained some head contributions. The channel manager can then use this meta-data to decide whether to reload the whole page instead of just replacing the markup of a container.