api: use wamp services instead of forwarding http requests for internal apis

Streetwriters.Common/Interfaces/IUserSubscriptionService.cs

@@ -0,0 +1,13 @@
+using System.Threading.Tasks;
+using Streetwriters.Common.Helpers;
+using Streetwriters.Common.Models;
+using WampSharp.V2.Rpc;
+
+namespace Streetwriters.Common.Interfaces
+{
+    public interface IUserSubscriptionService
+    {
+        [WampProcedure("co.streetwriters.subscriptions.subscriptions.get_user_subscription")]
+        Task<Subscription> GetUserSubscriptionAsync(string clientId, string userId);
+    }
+}