End-to-end testing

Here are the first working end-to-end tests. I'm using Protractor instead of ngScenario.
So now `npm test` will call the Karma unit tests and then the Protactor tests. Protractor needs both the NodeJs server and the Selenium server up, I've modified the Travis config file to take care of that.

Problems to be solved:
* Resetting the MongoDB database between tests. It might be a good idea to use a different database instead of `habitrpg` (e.g.: `habitrpg_test`), so the e2e test can be run against that it.
* Automatically start the Node and Selenium servers if they are not running when executing `npm test`. 

Any help is appreciated :)