Add "libgdx" unmanaged dependency.

Added an unmanaged dependency on libgdx (2013-06-22 build) for "core" and "desktop" projects. Libgdx doesn't seem to be published at the momemnt in repos easily available from sbt.
Added build definition file

Added Build.scala describing the main projects "hostilez" and two subprojects, "hostilez-core" and "hostilez-desktop". Added basic implementation of the Game and DesktopGame classes to have something runable.