add time zone support for sites and users

Oqtane.Client/Services/Interfaces/ITimeZoneService.cs

@@ -0,0 +1,18 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Oqtane.Models;
+
+namespace Oqtane.Services
+{
+    /// <summary>
+    /// Service to store and retrieve <see cref="TimeZone"/> entries
+    /// </summary>
+    public interface ITimeZoneService
+    {
+        /// <summary>
+        /// Get the list of time zones
+        /// </summary>
+        /// <returns></returns>
+        Task<List<TimeZone>> GetTimeZonesAsync();
+    }
+}

Oqtane.Client/Services/TimeZoneService.cs

@@ -0,0 +1,22 @@
+using System.Collections.Generic;
+using System.Net.Http;
+using System.Threading.Tasks;
+using Oqtane.Documentation;
+using Oqtane.Models;
+using Oqtane.Shared;
+
+namespace Oqtane.Services
+{
+    [PrivateApi("Don't show in the documentation, as everything should use the Interface")]
+    public class TimeZoneService : ServiceBase, ITimeZoneService
+    {
+        public TimeZoneService(HttpClient http, SiteState siteState) : base(http, siteState) { }
+
+        private string Apiurl => CreateApiUrl("TimeZone");
+
+        public async Task<List<TimeZone>> GetTimeZonesAsync()
+        {
+            return await GetJsonAsync<List<TimeZone>>($"{Apiurl}");
+        }
+    }
+}