Making the app source files available in the test directory (fixing #101)

Fixes #101. I have simply copied the solution [from generator-backbone](https://github.com/yeoman/generator-backbone/blob/12ebb0ad89c385c2c3d7a9c6fe5e37e7b2a903a3/app/templates/Gruntfile.js#L102), which is just what @kjarnet suggested.