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
Then let's delete it together with featureId if there is no associated layerId.
What do you think?
FYI: this is the current situation