Feature/setup protractor for testing

@bajtos 

Fixes #396
This contains too much copy-and-paste code to my taste. Can you please extract the shared code and simplify both tasks to something like this:

```js
gulp.task('test-client-e2e', function(callback) {
  execWithTestServer([
    'node_modules/.bin/protractor',
    'start',
    '--single-run',
    '--browsers',
    'PhantomJS',
    'client/test/integration/karma.integration.js',
  ], callback);
});
```

Also are you sure that `client/test/integration/karma.integration.js` is the correct config file for protractor?