Identifiers for lon-lat queries/clusters

[greenape]

We increasingly make use of 'clusters' of towers, but at present the only way to get these back via the api is to treat them as Lon-lats, which doesn't give you back the identifiers and makes it a pain to match them up to anything else done with the clusters. Be nice to fix this, and return any available identifier for lon-lat levels (possibly not if they are sensitive info).

[greenape]

In conjunction with reduced tables work.