Pathmanager update

These are the changes to PathManager from the multiplayer branch. I'm doing a pull request so it can be reviewed before being merged, as there are a couple of things to consider:

* Renamed the SAVED_WORLDS directory to 'worlds' and screens to 'screenshots' for consistency.
* By default Terasology uses the home directory rather than the install directory now.
* Added two more libraries - jna and platform to support the lookup of the proper windows home directory.

The upshot of this is existing saved games will not be found without users moving their files.