Added HelloWorld sample (copied from wiki)

The wiki ( https://github.com/box/box-java-sdk-v2/wiki/HelloWorld )
already has a sample app.  Checking that app into the SDK itself,
along with an Ant build.xml file to make it super easy to use.
Convert tabs to spaces in sample code
Merge pull request #22 from mmorearty/hello-world-sample

Added HelloWorld sample (copied from wiki)