[Refactor] Move SQL classes in their own assembly

BTCPayServer/Data/InvoiceDataExtensions.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using BTCPayServer.Services.Invoices;
+
+namespace BTCPayServer.Data
+{
+    public static class InvoiceDataExtensions
+    {
+        public static InvoiceState GetInvoiceState(this InvoiceData invoiceData)
+        {
+            return new InvoiceState(invoiceData.Status, invoiceData.ExceptionStatus);
+        }
+    }
+}