Transaction Deletion Added

Ability to delete CreditMemos, Estimates, Invoices, PurchaseOrders, and SalesReceipts (when using the QBOv3 API) have been added.  The new delete methods take a QuickBooks ID as a parameter and returns the ID that was deleted.  These methods have been tested, but not all of the QuickBooks objects that have can be deleted have been implemented (such as VendorCredit, TimeActivity, etc).