POM changes for 0.9 release

This contains the changes and the version bumps related to the first Maven Central (Sonatype) release 0.9.

Some notable changes:

- The building of the zip assemblies now only happens when the "hudson" profile is used.
- The default Maven repositories are now the Sonatype ones which are then overriden in the "hudson" profile to the ones of ardor3d.

As it's impossible to put git tags into a pull request, please create the `v0.9` tag for the commit 27979b9. (You can use GitHub's new "releases" functionality for that)