Added invoice export function and started implementation of unitofwork pattern (#43)

* complete read invoices from db

* wip

* wip

* wip

* wip

* wip

* wip

* wip

* wip

* updated nuget package spapi

* WIP

* wip, now test

* wip, jut need to fix tax inclusive line amounts not supported

* wip

* wip, before I f everything up

* no, it complies now, this is the one before I f everything up

* wip

* wip

* wip, logic ready for testing

* wip it builds!!!!

* wip tested, working, need to complete the gui section

* wip

* wip

* wip - created export invoice data delete, time for testing

* wip testing phase

* wip - delete function fully tested and working

* wip on to sorting out the issue with settlement invoices not tallying

* wip

* wip

* wip

* wip

* wip before I complete change the ReadInvoiceLineItem sections

* that appears to have worked, on with the main quest

* no it's doesn't work, saving before i remove the confusing cache system (just use a dictionary!!)

* wipping picadilli

* wip

* wip

* implemented uow on inovice export, now for testing

* wip

* wip all tested do invoice currency convertion fearure

* wip

* pretty much done so long as xero accepts the exported invoices

* Complete!

src/bnhtrade.Core/Data/Database/SKU/InsertSku.cs

@@ -1,7 +1,7 @@
 using FikaAmazonAPI.AmazonSpApiSDK.Models.ProductPricing;
 using System;
 using System.Collections.Generic;
-using System.Data.SqlClient;
+using Microsoft.Data.SqlClient;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
@@ -22,11 +22,11 @@ namespace bnhtrade.Core.Data.Database.Sku
                 var dbTax = new Data.Database.Account.ReadTaxCode();
                 var taxCodeList = dbTax.GetByTaxCodeId(new List<int> { accountTaxCodeId });
 
-                if (!taxCodeList.Any())
+                if (taxCodeList.ContainsKey(accountTaxCodeId) == false)
                 {
                     throw new Exception("AccountTaxCodeID=" + accountTaxCodeId + " doesn't exist!");
                 }
-                else if (taxCodeList[0].IsValidOnIncome == false)
+                else if (taxCodeList[accountTaxCodeId].IsValidOnIncome == false)
                 {
                     throw new Exception("AccountTaxCodeID=" + accountTaxCodeId + " is not a valid type for an SKU.");
                 }