Added qxmpp libs and implemented modular structure

- Added and configured qmpp libraries. Please note that I only have
tested the build on Mac OS X, so the build may not work in Windows or
Linux.
- Added a qChat example that shows you how to implement and use the LAN
Chat module in your app.
- Structural changes in the source code.
- Improvements and fixes in the QML interface.
- New XMPP login dialog in QML (WARNING: The app crashes when clicking
the login button in OS X due to a String-Related issue)