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
Unrelated to this PR, but I think 'features' is only used by our Application and is not documented. So we could change our app to sue 'featureidentify' and remove the 'features' type.