Add multithread support for content management.

TODO: merge similar thread pooling code & cleanup
credits: mikeagun for answering my random java questions
Update RAM config checks
Re-add check for existing files.
Merge branch 'master' of https://github.com/jianC/UnityLauncher
Some more bugfixes.
Center the window.

based on: http://www.codebeach.com/2008/02/center-dialog-box-frame-or-window-in.html
Merge pull request #6 from jianC/master

Fix