Add map settings to backend. Install leaflet assets to render maps.

app/views/admin/settings/_map_form.html.erb

@@ -0,0 +1,31 @@
+<div class="row">
+  <div class="small-12 column">
+    <div id="admin-map" class="map" data-map
+                        data-latitude="<%= Setting["map.latitude"] %>"
+                        data-longitude="<%= Setting["map.longitude"] %>"
+                        data-zoom="<%= Setting["map.zoom"] %>"
+                        data-tiles-attribution-selector="#admin-map-attribution"
+                        data-tiles-provider="//{s}.tile.osm.org/{z}/{x}/{y}.png"
+                        data-latitude-input-selector="#latitude"
+                        data-longitude-input-selector="#longitude"
+                        data-zoom-input-selector="#zoom"
+                        data-marker-selector="#admin-map-marker">
+    </div>
+    <div id="admin-map-attribution" class="map-attributtion">
+      &copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors
+    </div>
+
+    <%= form_tag admin_update_map_path, method: :put, id: 'map-form' do |f| %>
+
+      <%= hidden_field_tag :latitude,   Setting["map.latitude"] %>
+      <%= hidden_field_tag :longitude,  Setting["map.longitude"] %>
+      <%= hidden_field_tag :zoom,       Setting["map.zoom"] %>
+
+      <div class="small-12 medium-6 large-4">
+        <%= submit_tag t("admin.settings.index.map.form.submit"),
+                     class: "button hollow expanded" %>
+      </div>
+
+    <% end %>
+  </div>
+</div>