Order admin poll list by starts_at date

config/locales/en/admin.yml

@@ -921,6 +921,8 @@ en:
         create: "Create poll"
         name: "Name"
         dates: "Dates"
+        start_date: "Start Date"
+        closing_date: "Closing Date"
         geozone_restricted: "Restricted to districts"
       new:
         title: "New poll"

config/locales/es/admin.yml

@@ -921,6 +921,8 @@ es:
         create: "Crear votación"
         name: "Nombre"
         dates: "Fechas"
+        start_date: "Fecha de apertura"
+        closing_date: "Fecha de cierre"
         geozone_restricted: "Restringida a los distritos"
       new:
         title: "Nueva votación"