*FEEDBACK REQUESTED:*

This method is needed in the `Connectors` class when generating a `PathMappings` instance. I couldn't figure out a way to do this efficiently, so I thought it'd be better to just delegate this to the connector. A number of our (real) connectors can implement this by simply returning the identifier (which is also the path).

Note that I kept this method abstract, which means all Connector implementation classes will have to provide it. I toyed with providing a default implementation, but I thought it was important enough that developers know there's a new method and provide an efficient implementation. So if we go with this, However, I could be convinced that we should not break binary compatibility, and that we should provide a default implementation.

Thoughts?