Reversegeocoding for location search

Please merge https://github.com/geoadmin/service-sphinxsearch/pull/132

Don't forget that one has to update the indices in prod for the next deploy.
https://github.com/geoadmin/mf-chsdi3/issues/844
Nice refactoring here!

However, I would not set the attribute at all when _origin_to_layerbodid returns empty string. Clients might assume that if there is a layerBodId, it's usable.