Include associated waypoint title for routes in search index?

https://github.com/c2corg/v6_api/issues/90 was about including the title of the main waypoint in the title of a route. The titles of all associated waypoints could be included as well (e.g. in the summary or description).

> It would be nice if route-associated waypoints could be indexed as well (if not too complicated!? maybe in an evolution?) since it would help finding a route to be able to mention any of the summits the route goes through.
> https://github.com/c2corg/v6_api/issues/120#issuecomment-170884298