Allow avoidance of cobblestone

So far ferries, fords and steps can be avoided on the route. I'd be nice to be able to avoid cobblestone pavements on the route upon selection. This is a regular use case for navigation especially for inner-city routes.

Start by tracing how the existing ferry, ford, and steps avoidance options are implemented in the routing API. Identify where cobblestone pavement is represented and how route preferences are tested; done means a selected avoidance option prevents cobblestone segments from being used where alternatives exist.

Written by the indexing model from the issue text.