Add support for testing with Node

The primary purpose of this pull request is to add support for `mocha` testing on the command line. It provides an `environment` prompt allowing user to select `Node` or `browser`.

I have also added tests for the generator itself, as well as bumped the required version `yeoman-generator` that is required, as the newer version has access to the testing features documented on the [Yeoman testing page](http://yeoman.io/authoring/testing.html).