Added functionality to extract .pack.xz files. The npm modules available to do...

Added functionality to extract .pack.xz files. The npm modules available to do this were a mess, being either outdated or refusing to build on windows. In order to achieve this, I wrote up a small java library which will extract these files. We simply pass the files we want to extract to the command line using a corresponding argument and it does the rest. This should be no issue as we will always have a JRE present on this launcher, whether that be bundled or already installed.