feature: Server error provider added, client notification service added

WotBlitzStatisticsPro.Blazor/Services/INotificationsService.cs

@@ -0,0 +1,19 @@
+using System;
+using WotBlitzStatisticsPro.Blazor.Model;
+
+namespace WotBlitzStatisticsPro.Blazor.Services
+{
+    public interface INotificationsService
+    {
+        NotificationType Type { get; }
+
+        string Summary { get; }
+        string Message { get; }
+
+        event Action MessageArrived;
+
+        void ReportInfo(string summary, string message);
+        void ReportWarning(string summary, string message);
+        void ReportError(string summary, string message);
+    }
+}