noindex support for small results

- Added noindex_pages_with_fewer_than_n_results param
- If results is less than the noindex_pages_with_fewer_than_n_results param we insert noindex meta
	- `<meta name="robots" content="noindex, follow" />`

https://github.com/GigaOM/gigaom/issues/5221
Why add a new method instead of [using the existing](https://github.com/misterbisson/scriblio/blob/master/plugin/class-facets.php#L205)?