provide basic tool for building and testing through grunt

[obiot]

Now that we "master" grunt, I would like propose to add the required files for grunt and the following to the current boilerplate :

• a grunt task to build a minified version of the game (still useful for deployment)
• a grunt task to test the game using a local web-server (like grunt-phantom or others, i don't remember which other ones I saw so far).

[obiot]

duplicated