Improved test on the generated files

### Add a test suite on the generated files.

* Enable [coveralls.io](https://coveralls.io/r/eleven-labs/generator-gulp-angular)
* Yeoman you should shut up during test => thanks @MethodGrab [Gist mute.js](https://gist.github.com/MethodGrab/09f3431942ca14b6805d#file-mute-js)
* Create mocha test `test/test-files-generate.mocha.js`
 * For each scenario
 * assert file exist or not exist
 * assert contents of the files who are templating with LoDash: `bower.json`, `package.json`, `src/app/index.js`, `src/index.html`, `src/app/vendor.scss`, and gulp's tasks
(must be completed see [files.json](https://github.com/Swiip/generator-gulp-angular/blob/master/app/files.json#L24))

Tips: In Sublime Text go to `test/test-files-generate.mocha.js` and folding line with shortcut (`CTRL+K, CTRL+3`) you should see only `describe()` and `it()`

Screenshot: 
![mocha_output](https://cloud.githubusercontent.com/assets/3020368/4979380/a2c63a3a-68f6-11e4-8d37-fced37ae703e.png)

Travis CI build: https://travis-ci.org/eleven-labs/generator-gulp-angular/builds/40558096

Please community reviews this PR before merge !