Maven, SimpleXML and bugfixes

In order to get the SDK working with our system, we needed to port the build system from Ant to Maven.
While digging in the code, we were also able to fix some bugs and add some improvements to your SDK.

What we did is basiclly:
* Changed the build system from Ant to Maven
* Changed old staging-URLs to the correct ones
* Replaced SaX with [Simple XML](http://simple.sourceforge.net/)
* Return a response object (e.g. ```CreateResponse```) from a request instead of ```boolean```
* Bugfixes and performance improvements

If you have any questions, please feel free to ask.