[RFR] Bootstrap protractor tests

* add grunt `init` task which copy `config-dist.js` and `server-dist.json` to real files
* add grunt `json_server` task to launch a fake api with `server.json` datas on dev env
* include `json_server` start into `grunt` default task
* add grunt `protractor` task to launch tests with protractor
* include `protractor` into the grunt `test` task
* integrate `protractor` tests into Travis build (by using SauceLabs)
* write first very basic test and run it with chrome browser