Magento 1.8 support

I kept running into problems trying to connect to Magento 1.8.1.0, so I refactored the connector to use the latest WSDL. This resolved various problems such as the "login" operation not being present, etc. There might have been a less intrusive fix, but it looked like an update would be useful.

The modifications I made to pom.xml might not be useful to anyone else, but they're included just in case.