Gulp task to run protractor tests

Gulp task to start `protractor` tests. Before running tests it ensures webdriver is installed (`ensure_webdriver_standalone`) and starts it (`webdriver_standalone`).

Usage:
```
gulp test
```
> Even if it is only used once, we may want to keep requires at the top of the file for readability.

Good point. I was about to do this but I forgot.
> Why do you have to spawn a child process?

This task starts a webdriver we need to keep running during protractor does it's job. Thanks to `webdriver_standalone` task, a developer won't have to remember to start it in a different console window every time before he wants to run tests.