Option to Shutdown when Render Completes

Feature implementation for llbit/chunky#24

* Added checkbox on Advanced tab of Render controls labeled "Shutdown when render completes" 
  * Toggleable at any time during rendering
* Cancelable 30 second countdown before shutdown
* Amended documentation to enable functionality on Unix-based systems (Linux, BSD, OS X)
  * Requires use of `sudo` without password (so it doesn't need to prompt the user for it), instructs user to add `NOPASSWD:` directive for their username and /sbin/shutdown with `visudo`

Tested working on Debian Wheezy and Windows 7, both 64-bit.

Copied SystemUtils and JavaVersion classes, retaining attribution and license, from Apache Commons-Lang3 to facilitate robust detection of OS. JavaVersion was required to fix import errors in SystemUtils.

Merged with latest commit of llbit/chunky