Fixed the QBXML SalesOrder Class

- Matched the asQBXML signature to match its parent's asQBXML signature
- Inside asQBXML add a variable to grab the type of request (Add, Mod, or Query) so that could be added to the end of the "SalesOrderLine(Add)" tag.  You may want to update this section to detect the request type a different way, maybe via a parameter or something.  This works for now though.
- Modified the appropriate methods to add a SalesOrderLine.  It looks like it was copied from the InvoiceLine class and was never changed.
- Fixed bug in setAmount()