Update to use Gradle and libGDX v1.2.0

Moved project to the standard Gradle environment: created a whole new project using the gdx-setup.jar, then copied over the source files and assets.
Fixed the PackSkins class to use TexturePacker static functions.
Rebuilt the .pack file to reflect new 1.2.0 atlas file changes
Changed some path locations to better reflect libGDX standards
Fixed several issues from the migration such as replacing deprecated functions with correct ones