Use the new API return value for link trail/prefix

There's a new API return value (see gerrit change If617f43004dbd42f7) that we
should be using for trails and prefices, so I've added that to WikiConfig.

Change-Id: I875fa1f73619bdbaafd772663b8a3c4abdccb77f
Merge "Use the new API return value for link trail/prefix"