Headless QUnit - Run qunit tests from command line

This isn't quite done yet, but it's getting there. I know we still need to:

- [x] Fix the tests that were broken by upgrading qunit (empty test blocks are no longer allowed)
- [x] Include `rake test:qunit` in the `rake test` run so that all tests are run by `rake test`
- [x] Document how to install and set up phantomjs on Windows, Mac and Linux
- [x] When phantomjs is NOT installed, have the rake task give instructions on how to install it rather than breaking

Added [#2898](http://redmine.virtualworldframework.com/issues/2898) to account for the following Jenkins tasks:

- Install phantomjs on the jenkins server
- Include `rake test:qunit` in the jenkins run
- Make the result of `rake test:qunit` fail the build on jenkins

Refs [#1343](http://redmine.virtualworldframework.com/issues/1343)