consolidate Service interface and implementation classes

Oqtane.Client/Services/LocalizationService.cs

@@ -7,6 +7,18 @@ using Oqtane.Shared;
 
 namespace Oqtane.Services
 {
+    /// <summary>
+    /// Service to retrieve localizations (<see cref="Culture"/>)
+    /// </summary>
+    public interface ILocalizationService
+    {
+        /// <summary>
+        /// Returns a collection of supported cultures
+        /// </summary>
+        /// <returns></returns>
+        Task<IEnumerable<Culture>> GetCulturesAsync(bool installed);
+    }
+
     [PrivateApi("Don't show in the documentation, as everything should use the Interface")]
     public class LocalizationService : ServiceBase, ILocalizationService
     {