Make overpass server URL configurable

app/assets/javascripts/index/query.js

@@ -177,7 +177,7 @@ OSM.Query = function(map) {
     });
 
     $.ajax({
-      url: "http://overpass-api.de/api/interpreter",
+      url: OSM.OVERPASS_URL,
       method: "POST",
       data: {
         data: "[timeout:5][out:json];" + query,

app/assets/javascripts/osm.js.erb

@@ -8,6 +8,7 @@ OSM = {
   API_VERSION:           <%= API_VERSION.to_json %>,
   STATUS:                <%= STATUS.to_json %>,
   MAX_NOTE_REQUEST_AREA: <%= MAX_NOTE_REQUEST_AREA.to_json %>,
+  OVERPASS_URL:          <%= OVERPASS_URL.to_json %>,
 
   apiUrl: function (object) {
     var url = "/api/" + OSM.API_VERSION + "/" + object.type + "/" + object.id;

config/example.application.yml

@@ -84,6 +84,8 @@ defaults: &defaults
   require_terms_seen: false
   # Whether to require users to agree to the CTs before editing
   require_terms_agreed: false
+  # URL of Overpass instance to use for feature queries
+  overpass_url: http://overpass-api.de/api/interpreter
 
 development:
   <<: *defaults