added ability to add site through admin UI, fixed Logo control to not render of site does not have a logo, updated launchsettings so that port number is consistent for both IIS Express and .NET Core web server

Oqtane.Client/Services/ITenantService.cs

@@ -1,10 +1,13 @@
 using Oqtane.Models;
+using System.Collections.Generic;
 using System.Threading.Tasks;
 
 namespace Oqtane.Services
 {
     public interface ITenantService
     {
+        Task<List<Tenant>> GetTenantsAsync();
+
         Task<Tenant> GetTenantAsync();
     }
 }